Light detection device

ABSTRACT

A light detection device includes: a Fabry-Perot interference filter provided with a light transmission region; a light detector configured to detect light transmitted through the light transmission region; a package having an opening and accommodating the Fabry-Perot interference filter and the light detector, and a light transmitting unit arranged on an inner surface of the package so as to close an opening, the light transmitting unit including a band pass filter configured to transmit light incident on the light transmission region. When viewed from a direction parallel to the line, an outer edge of the Fabry-Pert interference filter is positioned outside an outer edge of the opening, and an outer edge of the light transmitting unit is positioned outside the outer edge of the Fabry-Perot interference filter.

TECHNICAL FIELD

The present disclosure relates to a light detection device including aFabry-Perot interference filter having a first mirror and a secondmirror, a distance therebetween is variable.

BACKGROUND ART

A light detection device including: a Fabry-Perot interference filterhaving a first mirror and a second mirror, a distance therebetween isvariable; a light detector for detecting light transmitted through theFabry-Perot interference filter; a package accommodating the Fabry-Perotinterference filter and the light detector; and a light transmittingunit arranged on an inner surface of the package so as to close anopening of the package is known (see Patent Literature 1, for example).

CITATION LIST Patent Literature

Patent Literature 1: WO 15/064758 A

SUMMARY OF INVENTION Technical Problem

From the viewpoint of improving the S/N ratio and resolution, in lightdetection devices as described above, it is quite important to suppressstray light (light not passing through the light transmission region ofthe Fabry-Perot interference filter) from entering the light detector.Moreover, since it is necessary to control the distance between a firstmirror and a second mirror with an extremely high accuracy in aFabry-Perot interference filter, it is extremely important to uniformizethe temperature in the package in order to suppress variations in thestress generated in the Fabry-Perot interference filter due to a changein the temperature in the use environment.

Therefore, one embodiment of the present disclosure aims at providing alight detection device having high light detecting characteristics.

Solution to Problem

A light detection device according to one embodiment of the presentdisclosure includes: a Fabry-Perot interference filter having a firstmirror and a second mirror, a distance therebetween is variable, andprovided with a light transmission region on a predetermined line, thelight transmission region configured to transmit light corresponding tothe distance between the first mirror and the second mirror, the lighttransmission region provided on a predetermined line; a light detectorarranged on a first side of the Fabry-Perot interference filter on theline, the light detector configured to detect light transmitted throughthe light transmission region; a package having an opening positioned ona second side of the Fabry-Perot interference filter on the line, thepackage configured to accommodate the Fabry-Perot interference filterand the light detector; and a light transmitting unit arranged on aninner surface of the package so as to close the opening and including aband pass filter configured to transmit light incident on the lighttransmission region, in which, when viewed from a direction parallel tothe line, an outer edge of the Fabry-Perot interference filter ispositioned outside an outer edge of the opening and an outer edge of thelight transmitting unit is positioned outside the outer edge of theFabry-Perot interference filter.

In this light detection device, the outer edge of the Fabry-Perotinterference filter is positioned outside the outer edge of the openingof the package, and the outer edge of the light transmitting unitincluding the band pass filter is positioned outside the outer edge ofthe Fabry-Perot interference filter. This can prevent light fromentering the package via a side surface (a surface excluding a lightincident surface and a light emitting surface facing each other in adirection parallel to the predetermined line in the light transmittingmember) of the light transmitting unit due to an incident angle of lightat the opening of the package, diffraction at the opening of thepackage, etc. and becoming stray light. Moreover, it is possible toprevent light, which has become stray light due to an incident angle oflight at the opening of the package, diffraction at the opening of thepackage, etc., from entering the light detector. Furthermore, forexample as compared to a case where the outer edge of the lighttransmitting unit is positioned inside the outer edge of the Fabry-Perotinterference filter, the heat capacity of the light transmitting unitand a thermally connected area between the light transmitting unit andthe package increases, and thus as a result the temperature in thepackage can be uniformized. As described above, the light detectiondevice has high light detecting characteristics.

In the light detection device according to one embodiment of the presentdisclosure, the light transmitting unit may further include a lighttransmitting member provided with a band pass filter, and the outer edgeof the light transmitting member may be positioned outside the outeredge of the Fabry-Perot interference filter when viewed from a directionparallel to the line. That is, the light detection device in this case(light detection device of the first aspect) includes: a Fabry-Perotinterference filter having a first mirror and a second mirror, adistance therebetween is variable, and provided with a lighttransmission region on a predetermined line, the light transmissionregion configured to transmit light corresponding to the distancebetween the first mirror and the second mirror, the light transmissionregion provided on a predetermined line; a light detector arranged onone side (first side) of the Fabry-Perot interference filter on theline, the light detector configured to detect light transmitted throughthe light transmission region; a package having an opening positioned onthe other side (second side) of the Fabry-Perot interference filter onthe line, the package configured to accommodate the Fabry-Perotinterference filter and the light detector; a light transmitting memberarranged on an inner surface of the package so as to close the opening;and a band pass filter provided to the light transmitting member, inwhich, when viewed from a direction parallel to the line, an outer edgeof the Fabry-Perot interference filter is positioned outside an outeredge of the opening, and an outer edge of the light transmitting memberis positioned outside the outer edge of the Fabry-Perot interferencefilter.

In the light detection device of the first aspect, the outer edge of theFabry-Perot interference filter is positioned outside the outer edge ofthe opening of the package, and the outer edge of the light transmittingmember is positioned outside the outer edge of the Fabry-Perotinterference filter. This can prevent light from entering the packagevia a side surface (a surface excluding a light incident surface and alight emitting surface facing each other in a direction parallel to thepredetermined line in the light transmitting member) of the lighttransmitting member due to an incident angle of light at the opening ofthe package, diffraction at the opening of the package, etc. andbecoming stray light. Moreover, it is possible to prevent light, whichhas become stray light due to an incident angle of light at the openingof the package, diffraction at the opening of the package, etc., fromentering the light detector. Furthermore, for example as compared to acase where the outer edge of the light transmitting member is positionedinside the outer edge of the Fabry-Perot interference filter, the heatcapacity of the light transmitting member and a thermally connected areabetween the light transmitting member and the package increases, andthus as a result the temperature in the package can be uniformized. Asdescribed above, in the light detection device of the first aspect,light detecting characteristics are enhanced.

In the light detection device of the first aspect, the outer edge of theband pass filter may be positioned outside the outer edge of theFabry-Perot interference filter when viewed from a direction parallel tothe line. This ensures that light incident on the light transmissionregion of the Fabry-Perot interference filter has passed through theband pass filter.

In the light detection device of the first aspect, the thickness of thelight transmitting member may be a value larger than or equal to a valueobtained by multiplying the distance between the Fabry-Perotinterference filter and the light transmitting member by 0.5. As aresult, since the heat capacity of the light transmitting member isincreased while the volume of the space in the package is reduced, thetemperature in the package can be further uniformized.

In the light detection device of the first aspect, the Fabry-Perotinterference filter may have a silicon substrate supporting the firstmirror and the second mirror, and the light detector may have an InGaAssubstrate formed with a photoelectric conversion region. The lightdetector having the InGaAs substrate formed with the photoelectricconversion region has a high sensitivity to light having a wavelengthwithin a range between 1200 nm and 2100 nm, for example, as compared tolight having a wavelength shorter than 1200 nm and light having awavelength longer than 2100 nm. However, the light detector has a highsensitivity to light having a wavelength shorter than 1200 nm ascompared with light having a wavelength longer than 2100 nm. Meanwhile,the silicon substrate has a higher absorptivity to light having awavelength shorter than 1200 nm as compared with light having awavelength of 1200 nm or more (although this depends on a manufacturingmethod, the thickness, and an impurity concentration of the siliconsubstrate, a high absorptivity is exhibited especially for light havinga wavelength shorter than 1100 nm). Therefore, with the aboveconfiguration, for example in a case where light having a wavelengthwithin the range between 1200 nm and 2100 nm should be detected, thesilicon substrate of the Fabry-Perot interference filter can be causedto function as a high-pass filter. As a result, it is possible tosecurely suppress detection of noise light (light having a wavelengthshorter than 1200 nm (in particular, shorter than 1100 nm) and lighthaving a wavelength longer than 2100 nm) by the light detector by thesynergistic effect with the band pass filter.

In the light detection device of the first aspect, the band pass filtermay be provided on the light emitting surface of the light transmittingmember. As a result, it is possible to prevent occurrence of a damagesuch as a scratch in the band pass filter due to external physicalinterference.

The light detection device of the first aspect may further include alead pin passing through the package and a wire electrically connectingthe terminal of the Fabry-Perot interference filter and the lead pin. Asdescribed above, in this light detection device, the outer edge of theFabry-Perot interference filter is positioned outside the outer edge ofthe opening of the package, and the outer edge of the light transmittingmember is positioned outside the outer edge of the Fabry-Perotinterference filter. Therefore, even if the wire bends, contact betweenthe wire and the package can be prevented.

A light detection device according to one embodiment of the presentdisclosure may further include a bonding member, in which the band passfilter may have a polygonal plate shape, the package may have a firstwall part formed with the opening, a second wall part facing the firstwall part with the Fabry-Perot interference filter, the band passfilter, and the light detector interposed therebetween, and acylindrical side wall part surrounding the Fabry-Perot interferencefilter, the band pass filter, and the light detector, the bonding membermay fix the band pass filter to an inner surface of the first wall part,and an outer edge of the band pass filter may be positioned outside theouter edge of the Fabry-Perot interference filter when viewed from adirection parallel to the line. That is, the light detection device inthis case (light detection device of the second aspect) includes: aFabry-Perot interference filter having a first mirror and a secondmirror, a distance therebetween is variable, and provided with a lighttransmission region on a predetermined line, the light transmissionregion configured to transmit light corresponding to the distancebetween the first mirror and the second mirror, the light transmissionregion provided on a predetermined line; a band pass filter arranged onone side (second side) of the Fabry-Perot interference filter on theline, the band pass filter of a polygonal plate shape configured totransmit light incident on the tight transmission region; an lightdetector arranged on the other side (first side) of the Fabry-Perotinterference filter on the line, the light detector configured to detectlight transmitted through the light transmission region; a packagehaving a first wall part formed with an opening (light incident opening)at a position on one side of the band pass filter on the line, a secondwall part facing the first wall part with the Fabry-Perot interferencefilter, the band pass filter, and the light detector interposedtherebetween, and a cylindrical side wall part surrounding theFabry-Perot interference filter, the band pass filter, and the lightdetector, and a bonding member configured to fix the band pass filter onan inner surface of the first wall part, in which, when viewed from adirection parallel to the line, an outer edge of the Fabry-Perotinterference filter is positioned outside an outer edge of the opening,and an outer edge of the band pass filter is positioned outside theouter edge of the Fabry-Perot interference filter.

In light detection devices described as those of the background art, forexample in order to obtain an optical spectrum for light in apredetermined wavelength range, it is necessary that a band pass filtertransmits only light in the wavelength range. That is, in order toimprove light detecting characteristics of the light detection device,it is important that the band pass filter functions properly. In thisrespect, in the light detection device of the second aspect, the sidewall part of the package has a cylindrical shape while the band passfilter has a polygonal plate shape. As a result, as compared to thedistance between each side surface (each surface excluding a lightincident surface and a light emitting surface facing each other in adirection parallel to the predetermined line in the light transmittingmember) of the band pass filter and an inner surface of the side wallpart, the distance between each corner part (corner part formed byadjacent side surfaces) and the inner surface of the side wall part issmaller. Therefore, the band pass filter fixed to the inner surface ofthe first wall part of the package is positioned with a high accuracy bythe respective corner parts. Here, for example in a case where a bandpass filter has a circular plate shape, if the diameter of the band passfilter is increased such that the distance between a side surface of theband pass filter and an inner surface of a side wall part becomessmaller in order to implement high-precision positioning of the bandpass filter, the following problem occurs. That is, since an area of alight incident surface of the band pass filter thermally connected to aninner surface of a first wall part of the package is increased, the bandpass filter is easily affected by heat (deformation or otherdisadvantages due to heat) from the package. On the other hand, if aband pass filter has a polygonal plate shape, an area of a lightincident surface of the band pass filter thermally connected to an innersurface of a first wall part of the package becomes smaller, for exampleas compared to the case where the band pass filter has a circular plateshape, and thus the band pass filter is less likely to be affected byheat from the package. Furthermore, since the outer edge of theFabry-Perot interference filter is positioned outside the outer edge ofthe opening and the outer edge of the band pass filter is positionedoutside the outer edge of the Fabry-Perot interference filter, it isensured that light incident on the light transmission region of theFabry-Perot interference filter has been transmitted through the bandpass filter. As described above, according to the light detection deviceof the second aspect, the band pass filter can appropriately function.

The light detection device of the second aspect may further include alight transmitting member arranged on the inner surface of the firstwall part so as to close the opening, in which the band pass filter maybe fixed to an inner surface of the light transmitting member by thebonding member, and the bonding member may be arranged over the entireregion of a light incident surface of the band pass filter facing theinner surface of the light transmitting member. According to thisconfiguration, since the bonding member is arranged over the entireregion of the light incident surface of the band pass filter, the bandpass filter is securely fixed to the inner surface of the first wallpart. Furthermore, even if air bubbles are generated in the bondingmember at the time of manufacturing, the air bubbles easily escape frombetween the side surfaces of the band pass filter and the inner surfaceof the side wall part, scattering, diffraction, and the like at thebonding member are suppressed. Moreover, according to thisconfiguration, since the light transmitting member is provided,airtightness of the package is improved. Furthermore, since the bandpass filter is fixed to the inner surface of the light transmittingmember, thermal influence from the package is unlikely to be received.

The light detection device of the second aspect may further include alight transmitting member arranged on the inner surface of the firstwall part so as to close the opening, in which the band pass filter maybe fixed to an inner surface of the light transmitting member by thebonding member, and the bonding member may not be arranged at a regionexcluding a corner region in a light incident surface of the band passfilter facing the inner surface of the light transmitting member but bearranged at the corner regions. According to this configuration, sincethe bonding member is not arranged at a region excluding a corner regionin the light incident surface of the band pass filter, scattering anddiffraction of light and the like at the bonding member are moresecurely suppressed. Moreover, according to this configuration, sincethe light transmitting member is provided, airtightness of the packageis improved. Furthermore, since the band pass filter is fixed to theinner surface of the light transmitting member and the bonding member isnot arranged at the region excluding a corner region in the lightincident surface of the band pass filter, a thermal influence from thepackage is further unlikely to be received.

In the light detection device of the second aspect, the band pass filtermay be fixed to the inner surface of the first wall part by the bondingmember, and the bonding member may be arranged at a region excluding anopposed region facing the opening in a light incident surface of theband pass filter facing the inner surface of the first wall part.According to this configuration, since the bonding member is arranged atthe region excluding an opposed region facing the opening in the lightincident surface of the band pass filter, the band pass filter issecurely fixed on the inner surface of the first wall part. Furthermore,even if air bubbles are generated in the bonding member at the time ofmanufacturing, the air bubbles easily escape not only from between theside surfaces of the band pass filter and the inner surface of the sidewall part but also from the opening, scattering, diffraction, and thelike at the bonding member are suppressed.

In the light detection device of the second aspect, the band pass filtermay be fixed to the inner surface of the first wall part by the bondingmember, and the bonding member may not be arranged at a region excludinga corner region in a light incident surface of the band pass filterfacing the inner surface of the first wall part but be arranged in thecorner region. According to this configuration, since the bonding memberis not arranged at a region excluding a corner region in the lightincident surface of the band pass filter, scattering and diffraction oflight and the like at the bonding member are more securely suppressed.

In the light detection device of the second aspect, the bonding membermay protrude outward from the outer edge of the band pass filter whenviewed from a direction parallel to the line, and a part of the bondingmember protruding outward from the outer edge of the band pass filtermay be in contact with a side surface of the band pass filter. Accordingto this configuration, the band pass filter is more securely fixed.

In the light detection device of the second aspect, the opening may havea circular shape when viewed from a direction parallel to the line.According to this configuration, the intensity profile of light incidenton the package is uniformized.

In the light detection device of the second aspect, the band pass filtermay have a rectangular plate shape. According to this configuration, itis possible to effectively suppress the thermal influence given to theband pass filter from the package while the stability in fixing of theband pass filter on the inner surface of the first wall part of thepackage is ensured.

In the light detection device of the second aspect, the package may bemade of a metal material. According to this configuration, airtightnessof the package is improved, and electrical shielding is facilitated.Note that in the case where the package is formed of a metal material,the thermal conductivity of the package is increased. However asdescribed above, since the side wall part of the package has acylindrical shape while the band pass filter has a polygonal plateshape, the band pass filter is unlikely to be affected by heat from thepackage.

Advantageous Effects of Invention

According to one embodiment of the present disclosure, a light detectiondevice having high light detecting characteristics can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a light detection device of a firstembodiment.

FIG. 2 is a plan view of the light detection device of FIG. 1.

FIG. 3 is a perspective view of a Fabry-Perot interference filter of thelight detection device of FIG. 1.

FIG. 4 is a cross-sectional view of the Fabry-Perot interference filtertaken along line IV-IV in FIG. 3.

FIG. 5 is a cross-sectional view of a light detection device of a secondembodiment.

FIG. 6 is a cross-sectional view of a modification of the lightdetection device of the second embodiment.

FIG. 7 is a cross-sectional view of a light detection device accordingto a third embodiment.

FIG. 8 is an enlarged view of a part of the light detection device ofFIG. 7.

FIG. 9 is a plan view of the light detection device of FIG. 7.

FIG. 10 is a perspective view of a Fabry-Perot interference filter ofthe light detection device of FIG. 7.

FIG. 11 is a cross-sectional view of the Fabry-Perot interference filtertaken along line XI-XI in FIG. 10.

FIG. 12 is a cross-sectional view of a light detection device of afourth embodiment.

FIG. 13 is a plan view of the light detection device of FIG. 12.

FIG. 14 is a cross-sectional view of a light detection device of a fifthembodiment.

FIG. 15 is a plan view of the light detection device of FIG. 14.

FIG. 16 is a cross-sectional view of a light detection device of a sixthembodiment.

FIG. 17 is a plan view of the light detection device of FIG. 16.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the drawings. Note that the same orcorresponding parts in the respective drawings are denoted with the samesymbol, and overlapping descriptions are omitted.

First Embodiment [Configuration of Light Detection Device]

As illustrated in FIG. 1, a light detection device 1A includes a package2. The package 2 is a CAN package having a stem 3 and a cap 4. The cap 4is integrally formed by a side wall 5 and a top wall 6. The top wall 6faces the stem 3 in a direction parallel to a predetermined line L. Thestem 3 and the cap 4 are made of metal, for example, and are airtightlyjoined to each other.

On an inner surface 3 a of the stem 3, a wiring substrate 7 is fixed. Asa material of the wiring substrate 7, for example, silicon, ceramic,quartz, glass, plastic, or other materials can be used. On the wiringsubstrate 7, a temperature compensating element (not illustrated) suchas a light detector 8 and a thermistor is mounted. The light detector 8is arranged on the line L. More specifically, the light detector 8 isarranged such that the center line of a light receiving unit thereofcoincides with the line L. The light detector 8 is an infrared detectorsuch as a quantum type sensor using InGaAs or other compounds or athermal type sensor using a thermopile or a bolometer or otherinstruments. In a case where light of different wavelength regions ofultraviolet, visible, and near infrared regions, for example a siliconphotodiode or other components can be used as the light detector 8. Notethat the light detector 8 may include one light receiving unit or mayinclude a plurality of light receiving units in an arrayed shape.Furthermore, a plurality of light detectors 8 may be mounted on thewiring substrate 7.

On the wiring substrate 7, a plurality of spacers 9 are fixed. As amaterial of the spacers 9, for example, silicon, ceramic, quartz, glass,plastic, or other materials can be used. On the plurality of spacers 9,a Fabry-Perot interference filter 10 is fixed by, for example, anadhesive agent. The Fabry-Perot interference filter 10 is arranged onthe line L. More specifically, the Fabry-Perot interference filter 10 isarranged such that the center line of a light transmission region 1.acoincides with the line L. Note that the spacers 9 may be integrallyformed with the wiring substrate 7. The Fabry-Perot interference filter10 may be supported not by the plurality of spacers 9 but by one spacer9.

A plurality of lead pins 11 are fixed to the stem 3. More specifically,each of the lead pins 11 penetrates through the stem 3 in a state whereelectrical insulation and airtightness with the stem 3 is maintained.Electrode pads provided on the wiring substrate 7, terminals of thelight detector 8, terminals of the temperature compensating element, andterminals of the Fabry-Perot interference filter 10 are electricallyconnected to the respective lead pins 11 by wires 12. This enables inputand output of electric signals to and from each of the light detector 8,the temperature compensating element, and the Fabry-Perot interferencefilter 10.

The package 2 includes an opening 2 a. More specifically, the opening 2a is included in the top wall 6 of the cap 4 such that the center linethereof coincides with the line L. On an inner surface 6 a of the topwall 6, a light transmitting member 13 is arranged so as to close theopening 2 a. The light transmitting member 13 is airtightly joined tothe inner surface 6 a of the top wall 6. The light transmitting member13 transmits light at least in a range of measurement wavelengths of thelight detection device 1A. The light transmitting member 13 is aplate-like member including a light incident surface 13 a and a lightemitting surface 13 b that face each other in a direction parallel tothe line L and side surfaces 13 c. The light transmitting member 13 ismade of, for example, glass, quartz, silicon, germanium, plastic, orother materials.

A band pass filter 14 is provided on the light emitting surface 13 b ofthe light transmitting member 13. The band pass filter 14 is arranged onthe light emitting surface 13 b of the light transmitting member 13 by,for example, vapor deposition, pasting, or other means. The band passfilter 14 selectively transmits light in a range of measurementwavelengths of the light detection device 1A. The band pass filter 14 isa dielectric multilayer film formed by a combination of a highrefractive material such as TiO₂ and Ta₂O₅ and a low refractive materialsuch as SiO₂ and MgF₂.

In the light detection device 1A, the light transmitting member 13 andthe band pass filter 14 form the light transmitting unit 100. That is,the light transmitting unit 100 includes the band pass filter 14 thattransmits light incident on the light transmission region 10 a of theFabry-Perot interference filter 10.

In the light detection device 1A, the package 2 accommodates the wiringsubstrate 7, the light detector 8, the temperature compensating element(not illustrated), the plurality of spacers 9, and the Fabry-Perotinterference filter 10. In the package 2, the light detector 8 ispositioned on one side (first side) of the Fabry-Perot interferencefilter 10 on the line L, and the opening 2 a and the light transmittingmember 13 are positioned on the other side (second side) of theFabry-Perot interference filter 10 on the line L.

A thickness T of the light transmitting member 13 (thickness in adirection parallel to the line L, which is a distance between the lightincident surface 13 a and the light emitting surface 13 b) is greaterthan or equal to a value obtained by multiplying a distance D1 betweenthe Fabry-Perot interference filter 10 and the light transmitting member13 (distance between a surface of the Fabry-Perot interference filter 10on the light transmitting member 13 side and the light emitting surface13 b of the light transmitting member 13) by 0.5. Moreover, thethickness T of the light transmitting member 13 is greater than or equalto a distance D2 between the Fabry-Perot interference filter 10 and thelight detector 8 (distance between a surface of the Fabry-Perotinterference filter 10 on the light detector 8 side and a surface of thelight detector 8 on the Fabry-Perot interference filter 10 side).

The positional relationship and sizes of the respective components whenviewed from a direction parallel to the line L are as follows. Asillustrated in FIG. 2, the center line of the opening 2 a, the centerline of the light transmitting member 13, the center line of the bandpass filter 14, the center line of the light transmission region 10 a ofthe Fabry-Perot interference filter 10, and the center line of the lightreceiving unit of the light detector 8 coincides with the line L. Theopening 2 a and an outer edge of the light transmission region 10 a ofthe Fabry-Perot interference filter 10 are, for example, circular. Theouter edges of the light transmitting member 13, the band pass filter14, the Fabry-Perot interference filter 10, and the light detector 8are, for example, rectangular.

The outer edge of the light transmission region 10 a of the Fabry-Perotinterference filter 10 is positioned outside the outer edge of the lightdetector 8. The outer edge of the opening 2 a is positioned outside theouter edge of the light transmission region 10 a of the Fabry-Perotinterference filter 10. The outer edge of the band pass filter 14 ispositioned outside the outer edge of the opening 2 a. The outer edge ofthe Fabry-Perot interference filter 10 is positioned outside the outeredge of the opening 2 a. The outer edge of the Fabry-Perot interferencefilter 10 is positioned outside the outer edge of the light detector 8.The outer edge of the band pass filter 14 is positioned outside theouter edge of the Fabry-Perot interference filter 10. The outer edge ofthe light transmitting member 13 is positioned outside the outer edge ofthe Fabry-Perot interference filter 10. In the light detection device1A, the outer edge of the light transmitting member 13 and the outeredge of the band pass filter 14 coincide with each other. Note that “oneouter edge is positioned outside another outer edge when viewed from apredetermined direction” means that “the outer edge surrounds the otherouter edge when viewed from the predetermined direction” or that “theouter edge includes the other outer edge when viewed from thepredetermined direction”.

In the light detection device 1A configured as described above, whenlight enters the light transmission region 10 a of the Fabry-Perotinterference filter 10 from the outside via the opening 2 a, the lighttransmitting member 13, and the band pass filter 14, light having apredetermined wavelength is selectively transmitted (details will bedescribed later). The light transmitted through the light transmissionregion 10 a of the Fabry-Perot interference filter 10 enters the lightreceiving unit of the light detector 8 and is detected by the lightdetector 8.

[Configuration of Fabry-Perot Interference Filter]

As illustrated in FIG. 3, in the Fabry-Perot interference filter 10, alight transmission region 10 a that transmits light corresponding to thedistance between a first mirror and a second mirror is included on theline L. In the light transmission region 10 a, the distance between thefirst mirror and the second mirror is controlled with an extremely highaccuracy. That is, in the Fabry-Perot interference filter 10, the lighttransmission region 10 a is a region in which the distance between thefirst mirror and the second mirror can be controlled to a predetermineddistance in order to selectively transmit light having a predeterminedwavelength and is a region through which light having a predeterminedwavelength corresponding to the distance between the first mirror andthe second mirror can be transmitted.

As illustrated in FIG. 4, the Fabry-Perot interference filter 10includes a substrate 21. On a surface 21 a of the substrate 21 on alight incident side, an antireflection layer 31, a first laminated body32, an intermediate layer 33, and a second laminated body 34 arelaminated in the order mentioned. A gap (air gap) S is formed betweenthe first laminated body 32 and the second laminated body 34 by theintermediate layer 33 of a frame shape. The substrate 21 is made of, forexample, silicon, quartz, glass, or other materials. In a case where thesubstrate 21 is made of silicon, the antireflection layer 31 and theintermediate layer 33 are made of, for example, silicon oxide. Thethickness of the intermediate layer 33 may be an integral multipleobtained by multiplying the central transmission wavelength (that is,the central wavelength of a wavelength range that the Fabry-Perotinterference filter 10 can transmit) by ½.

A part of the first laminated body 32 corresponding to the lighttransmission region 10 a functions as a first mirror 35. The firstmirror 35 is supported on the substrate 21 via the antireflection layer31. The first laminated body 32 includes a plurality of polysiliconlayers and a plurality of silicon nitride layers with each of theplurality of layers laminated alternately. The optical thickness of eachof the polysilicon layers and the silicon nitride layers forming thefirst mirror 35 may be an integral multiple obtained by multiplying thecentral transmission wavelength by ¼. Note that a silicon oxide layermay be used instead of the silicon nitride layer.

A part of the second laminated body 34 corresponding to the lighttransmission region 10 a functions as a second mirror 36 facing thefirst mirror 35 via the gap S. The second mirror 36 is supported on thesubstrate 21 via the antireflection layer 31, the first laminated body32, and the intermediate layer 33. The second laminated body 34 includesa plurality of polysilicon layers and a plurality of silicon nitridelayers with each of the plurality of layers laminated alternately. Theoptical thickness of each of the polysilicon layers and the siliconnitride layers forming the second mirror 36 may be an integral multipleobtained by multiplying the central transmission wavelength by ¼. Notethat a silicon oxide layer may be used instead of the silicon nitridelayer.

In a part of the second laminated body 34 corresponding to the gap S, aplurality of through holes (not illustrated) extending from a surface 34a of the second laminated body 34 to the gap S is included. Theplurality of through holes is formed to an extent that the holes do notsubstantially affect the function of the second mirror 36. The pluralityof through holes have been used to form the gap S by removing apart ofthe intermediate layer 33 by etching.

In the first mirror 35, a first electrode 22 is formed so as to surroundthe light transmission region 10 a. In the first mirror 35, a secondelectrode 23 is formed so as to include the light transmission region 10a. The first electrode 22 and the second electrode 23 are formed bydoping the polysilicon layer with an impurity to reduce the resistance.The size of the second electrode 23 may be a size including the entirelight transmission region 10 a or may be substantially the same size asthat of the light transmission region 10 a.

On the second mirror 36, a third electrode 24 is formed. The thirdelectrode 24 faces the first electrode 22 and the second electrode 23via the gap S in a direction parallel to the line L. The third electrode24 is formed by doping the polysilicon layer with an impurity to reducethe resistance,

In the Fabry-Perot interference filter 10, the second electrode 23 ispositioned on the side opposite to the third electrode 24 with respectto the first electrode 22 in a direction parallel to the line L. Thatis, the first electrode 22 and the second electrode 23 are notpositioned on the same plane in the first mirror 35. The secondelectrode 23 is farther from the third electrode 24 than the firstelectrode 22 is.

A pair of terminals 25 are provided so as to face each other whileinterposing the light transmission region 10 a. Each of the terminals 25is arranged in a through hole extending from a surface 34 a of thesecond laminated body 34 to the first laminated body 32. Each of theterminals 25 is electrically connected to the first electrode 22 viawiring 22 a.

A pair of terminals 26 are provided so as to face each other whileinterposing the light transmission region 10 a. Each of the terminals 26is arranged in a through hole extending from the surface 34 a of thesecond laminated body 34 to a layer before the intermediate layer 33.Each of the terminals 26 is electrically connected to the secondelectrode 23 via wiring 23 a and is also electrically connected to thethird electrode 24 via wiring 24 a. Note that, a direction in which thepair of terminals 25 face each other and a direction in which the pairof terminals 26 face each other are perpendicular to each other (seeFIG. 3).

Trenches 27 and 28 are included on the surface 32 a of the firstlaminated body 32. A trench 27 annularly extends so as to surround thewiring 23 a extending from a terminal 26 along a direction parallel tothe line L. The trench 27 electrically insulates the first electrode 22from the wiring 23 a. A trench 28 annularly extends along the inner edgeof the first electrode 22. The trench 28 electrically insulates thefirst electrode 22 from a region inside the first electrode 22. Regionsinside the trenches 27 and 28 may be made of an insulating material orvoid.

Trenches 29 are included on the surface 34 a of the second laminatedbody 34. A trench 29 annularly extends so as to surround a terminal 25.The trench 29 electrically insulates the terminal 25 from the thirdelectrode 24. A region inside the trench 28 may be made of an insulatingmaterial or void.

On a surface 21 b of the substrate 21 on a light emitting side, anantireflection layer 41, a third laminated body 42, an intermediatelayer 43, and a fourth laminated body 44 are laminated in the ordermentioned. The antireflection layer 41 and the intermediate layer 43have a similar configuration to those of the antireflection layer 31 andthe intermediate layer 33, respectively. The third laminated body 42 andthe fourth laminated body 44 have lamination configurations symmetricalto those of the first laminated body 32 and the second laminated body34, respectively, with respect to the substrate 21. The antireflectionlayer 41, the third laminated body 42, the intermediate layer 43, andthe fourth laminated body 44 have a function of suppressing warping ofthe substrate 21.

The antireflection layer 41, the third laminated body 42, theintermediate layer 43, and the fourth laminated body 44 include anopening 40 a so as to include the light transmission region 10 a. Theopening 40 a has substantially the same diameter as the size of thelight transmission region 10 a. The opening 40 a is open on the lightemitting side while a bottom surface of the opening 40 a reaches theantireflection layer 41. A light shielding layer 45 is formed on asurface of the fourth laminated body 44 on the light emitting side. Thelight shielding layer 45 is made of, for example, aluminum. A protectivelayer 46 is formed on a surface of the light shielding layer 45 and aninner surface of the opening 40 a. The protective layer 46 is made of,for example, aluminum oxide. Note that, by setting the thickness of theprotective layer 46 at 1 to 100 nm (preferably, about 30 nm), opticalinfluence by the protective layer 46 can be negligible.

In the Fabry-Perot interference filter 10 configured in the abovemanner, when a voltage is applied between the first electrode 22 and thethird electrode 24 via the respective terminals 25 and 26, electrostaticforce corresponding to the voltage is generated between the firstelectrode 22 and the third electrode 24. Due to the electrostatic force,the second mirror 36 is attracted to the side of the first mirror 35fixed to the substrate 21, and the distance between the first mirror 35and the second mirror 36 is adjusted. As described above, in theFabry-Perot interference filter 10, the distance between the firstmirror 35 and the second mirror 36 is allowed to be variable.

The wavelength of light transmitted through the Fabry-Perot interferencefilter 10 depends on the distance between the first mirror 35 and thesecond mirror 36 in the light transmission region 10 a. Therefore, byadjusting the voltage applied between the first electrode 22 and thethird electrode 24, a wavelength of transmitted light can be selected asappropriate. At this time, the second electrode 23 has the samepotential as that of the third electrode 24. Therefore, the secondelectrode 23 functions as a compensation electrode for keeping the firstmirror 35 and the second mirror 36 flat in the light transmission region10 a.

The light detection device 1A can obtain an optical spectrum bydetecting light transmitted through the light transmission region 10 aof the Fabry-Perot interference filter 10 by the light detector 8 whilechanging the voltage applied to the Fabry-Perot interference filter 10(that is, changing the distance between the first mirror 35 and thesecond mirror 36 in the Fabry-Perot interference filter 10).

[Actions and Effects]

In the light detection device 1A, the outer edge of the Fabry-Perotinterference filter 10 of a chip shape is positioned outside the outeredge of the opening 2 a of the package 2, and the outer edge (outer edgeof the light transmitting unit 100) of the light transmitting member 13is positioned outside the outer edge of the Fabry-Perot interferencefilter 10. This can prevent light from entering the package 2 via theside surfaces 13 c of the light transmitting member 13 due to anincident angle of light at the opening 2 a, diffraction at the opening 2a, etc. and becoming stray light. This can further prevent light, whichhas become stray light due to an incident angle of light at the opening2 a, diffraction at the opening 2 a, etc., from entering the lightdetector 8. Furthermore, for example as compared to a case where theouter edge of the light transmitting member 13 is positioned inside theouter edge of the Fabry-Perot interference filter 10, the heat capacityof the light transmitting member 13 and a thermally connected areabetween the light transmitting member 13 and the package 2 increases,and thus as a result the temperature in the package 2 can beuniformized. As described above, light detecting characteristics areimproved in the light detection device 1A.

The prevention of stray light from entering the light detector 8 will bedescribed in more detail. A part of light entering the opening 2 a ofthe package 2 may be emitted from the side surfaces 13 c of the lighttransmitting member 13 into the package 2 due to an incident angle oflight at the opening 2 a, diffraction at the side surface of the opening2 a and at an emitting side corner (corer where the side surface of theopening 2 a meets the inner surface 6 a of the top wall 6), etc. Whensuch light is multiple-reflected within the package 2 and enters thelight detector 8, this appears as noise due to stray light in an outputsignal, which leads to degradation of light detecting characteristics.In particular, since the side surfaces 13 c of the light transmittingmember 13 are often rougher than the light incident surface 13 a and thelight emitting surface 13 b in many cases, light emitted from the sidesurfaces 13 c of the light transmitting member 13 into the package 2 islikely to be scattered and to enter the light detector 8. In contrast,in the light detection device 1A, the outer edge of the Fabry-Perotinterference filter 10 is positioned outside the outer edge of theopening 2 a of the package 2, and the outer edge of the lighttransmitting member 13 is positioned outside the outer edge of theFabry-Perot interference filter 10. As a result, for example as comparedwith the case where the outer edge of the light transmitting member 13is positioned inside the outer edge of the Fabry-Perot interferencefilter 10, the side surfaces 13 c of the light transmitting member 13are positioned apart from the light transmission region 10 a of theFabry-Perot interference filter 10 and the light detector 8. Therefore,the incidence of stray light on the light detector 8 is suppressed, andthe S/N ratio and the resolution are improved.

The uniformizing of the temperature in the package 2 will be describedmore specifically. When the opening 2 a of the package 2 becomessmaller, the volume of the package 2 itself becomes larger. Meanwhile,when the light transmitting member 13 is increased in size, the heatcapacity of the light transmitting member 13 and a thermally connectedarea between the light transmitting member 13 and the package 2 areincreased while the volume of the space in the package 2 is reduced. Asa result, the following actions are obtained. First, the volume of thepackage 2 itself, which is made of metal, has a high thermalconductivity, and is easily maintained at a uniform temperature as awhole (heat easily spreads to the whole), is increased. Furthermore,since the thermally connected area between the light transmitting member13 and the package 2 is large, heat is easily conducted from the package2 to the light transmitting member 13, and the light transmitting member13 is maintained at a uniform temperature with the package 2.Furthermore, since the volume of the space in the package 2 is small,the temperature of the space in the package 2 (and the constituentelements of the Fabry-Perot interference filter 10 and the like arrangedtherein) is also maintained at a uniform temperature by the influence ofthe package 2 and the light transmitting member 13 the temperature ofwhich is maintained at a uniform temperature. Furthermore, temporalchange in the temperature is suppressed by the light transmitting member13 and the package 2 having a large heat capacity. By these actions, thetemperature in the package 2 becomes thermally uniform, and the thermalcharacteristic of the light detection device 1A is stabilized.

Moreover, in the light detection device 1A, the outer edge of the bandpass filter 14 is positioned outside the outer edge of the Fabry-Perotinterference filter 10 when viewed from a direction parallel to the lineL. As a result, it is ensured that light incident on the lighttransmission region 10 a of the Fabry-Perot interference filter 10 hasbeen transmitted by the band pass filter 14.

The outer edge of the light transmission region 10 a of the Fabry-Perotinterference filter 10 is positioned outside the outer edge of the lightdetector 8. The outer edge of the opening 2 a is positioned outside theouter edge of the light transmission region 10 a of the Fabry-Perotinterference filter 10. The outer edge of the band pass filter 14 ispositioned outside the outer edge of the opening 2 a. As a result, it isensured that light incident on the light detector 8 via the opening 2 aand the light transmission region 10 a of the Fabry-Perot interferencefilter 10 has been transmitted by the band pass filter 14.

The outer edge of the Fabry-Perot interference filter 10 is positionedoutside the outer edge of the light detector 8. This can prevent lightnot transmitted by the light transmission region 10 a of the Fabry-Perotinterference filter 10 from entering the light detector 8 as straylight.

Moreover, in the light detection device 1A, the thickness T of the lighttransmitting member 13 is a value larger than or equal to a valueobtained by multiplying the distance D1 between the Fabry-Perotinterference filter 10 and the light transmitting member 13 by 0.5. As aresult, since the heat capacity of the light transmitting member 13 isincreased while the volume of the space in the package 2 is reduced, thetemperature in the package 2 can be further uniformized. Furthermore,since the light transmitting member 13 moves relatively closer to theFabry-Perot interference filter 10, this can prevent light nottransmitted by the light transmission region 10 a of the Fabry-Perotinterference filter 10 from entering the light detector 8 as straylight. Note that, in order to further uniformize the temperature in thepackage 2 and to further suppress incidence of stray light on the lightdetector 8, it is preferable that the thickness T is a value larger thanor equal to a value obtained by multiplying the distance D1 by 0.7, morepreferably, a value greater than or equal to the distance D1.

Moreover, in the light detection device 1A, the thickness T of the lighttransmitting member 13 is a value larger than or equal to the distanceD2 between the Fabry-Perot interference filter 10 and the light detector8. As a result, since the heat capacity of the light transmitting member13 is increased while the volume of the space in the package 2 isreduced, the temperature in the package 2 can be further uniformized.

In the light detection device 1A, the band pass filter 14 is provided onthe light emitting surface 13 b of the light transmitting member 13. Asa result, it is possible to prevent occurrence of a damage such as ascratch in the band pass filter 14 due to external physicalinterference.

In the light detection device 1A, the terminals 25 and 26 of theFabry-Perot interference filter 10 and the lead pins 11 are electricallyconnected by wires 12. As described above, in the light detection device1A, the outer edge of the Fabry-Perot interference filter 10 ispositioned outside the outer edge of the opening 2 a of the package 2,and the outer edge of the light transmitting member 13 is positionedoutside the outer edge of the Fabry-Perot interference filter 10.Therefore, even if the wires 12 bend, contact between the wires 12 andthe package 2 can be prevented.

Prevention of contact between the wires 12 and the package 2 will bedescribed more specifically. When a wire 12 is brought into contact withthe package 2 made of metal, an electric signal for controlling theFabry-Perot interference filter 10 also flows in the package 2, whichmakes it difficult to control the Fabry-Perot interference filter 10.Contrary to this, even when a wire 12 is brought into contact with thelight transmitting member 13 made of an insulating material, an electricsignal for controlling the Fabry-Perot interference filter 10 does notflow in the light transmitting member 13, and thus the Fabry-Perotinterference filter 10 can be controlled with a high accuracy. The aboveconfiguration that can prevent contact between the wires 12 and thepackage 2 is important.

Furthermore, in the light detection device 1A, a silicon substrate isadopted as the substrate 21 of the Fabry-Perot interference filter 10,and an InGaAs substrate formed with a photoelectric conversion region isadopted as the light detector 8, whereby the following actions andeffects are achieved. The light detector 8 having the InGaAs substrateformed with the photoelectric conversion region has a high sensitivityto light having a wavelength within a range between 1200 nm and 2100 nm,for example, as compared to light having a wavelength shorter than 1200nm and light having a wavelength longer than 2100 nm. However, the lightdetector 8 has a high sensitivity to light having a wavelength shorterthan 1200 nm as compared with light having a wavelength longer than 2100nm. Meanwhile, the silicon substrate has a higher absorptivity to lighthaving a wavelength shorter than 1200 nm as compared with light having awavelength of 1200 nm or more (although this depends on a manufacturingmethod, the thickness, and an impurity concentration of the siliconsubstrate, a high absorptivity is exhibited especially for light havinga wavelength shorter than 1100 nm). Therefore, with the aboveconfiguration, for example in a case where light having a wavelengthwithin the range between 1200 nm and 2100 nm should be detected, thesilicon substrate of the Fabry-Perot interference filter 10 can becaused to function as a high-pass filter. As a result, it is possible tosecurely suppress detection of noise light (light having a wavelengthshorter than 1200 nm (in particular, shorter than 1100 nm) and lighthaving a wavelength longer than 2100 nm) by the light detector 8 by thesynergistic effect with the band pass filter 14.

Second Embodiment [Configuration of Light Detection Device]

As illustrated in FIG. 5, a light detection device 1B is different fromthe light detection device 1A described above in configurations of alight transmitting member 13 and a band pass filter 14. In the lightdetection device 11, a light transmitting member 13 arranged on an innersurface of a package 2 extends to the inside the opening 2 a and aninner surface 5 a of a side wall 5. A light incident surface 13 a of thelight transmitting member 13 is substantially flush with an outersurface of a top wall 6 at the opening 2 a. Such a light transmittingmember 13 is formed by arranging a glass pellet inside a cap 4 with theopening 2 a facing down and melting the glass pellet. That is, the lighttransmitting member 13 is made of fused glass. A band pass filter 14extends to a part of the inner surface 5 a of the side wall 5 of the cap4 from a light emitting surface 13 b of the light transmitting member13.

In the light detection device 1B as well, like in the light detectiondevice 1A as described above, the light transmitting member 13 and theband pass filter 14 form the light transmitting unit 100. That is, thelight transmitting unit 100 includes the band pass filter 14 thattransmits light incident on the light transmission region 10 a of theFabry-Perot interference filter 10.

Also in the light detection device 1B, the thickness T of the lighttransmitting member 13 is a value larger than or equal to a valueobtained by multiplying the distance D1 between the Fabry-Perotinterference filter 10 and the light transmitting member 13 by 0.5.Moreover, the thickness T of the light transmitting member 13 is largerthan or equal to a distance D2 between the Fabry-Perot interferencefilter 10 and the light detector 8.

Furthermore, an outer edge of the light transmission region 10 a of theFabry-Perot interference filter 10 is positioned outside an outer edgeof the light detector 8. The outer edge of the opening 2 a is positionedoutside the outer edge of the light transmission region 10 a of theFabry-Perot interference filter 10. The outer edge of the band passfilter 14 is positioned outside the outer edge of the opening 2 a. Theouter edge of the Fabry-Perot interference filter 10 is positionedoutside the outer edge of the opening 2 a. The outer edge of theFabry-Perot interference filter 10 is positioned outside the outer edgeof the light detector 8. The outer edge of the band pass filter 14 ispositioned outside the outer edge of the Fabry-Perot interference filter10. The outer edge of the light transmitting member 13 is positionedoutside the outer edge of the Fabry-Perot interference filter 10.

[Actions and Effects]

Similar actions and effects as those of the light detection device 1Adescribed above are also achieved by the light detection device 11.Particularly, since the side surfaces 13 c of the light transmittingmember 13 extends to the inner surface 5 a of the side wall 5, it ispossible to further securely suppress light from entering the package 2via the side surfaces 13 c of the light transmitting member 13 due to anincident angle of light at the opening 2 a, diffraction at the opening 2a, etc. and becoming stray light. Furthermore, since the heat capacityof the light transmitting member 13 and a thermally connected areabetween the light transmitting member 13 and the package 2 areincreased, the temperature inside the package 2 can be furtheruniformized as a result.

Moreover, in the light detection device 1B, since the volume(particularly the thickness T) of the light transmitting member 13 islarge, flatness of the light incident surface 13 a and the lightemitting surface 13 b of the light transmitting member 13 made of fusedglass can be improved. Furthermore, even if air bubbles generated at thetime of formation remain in the light transmitting member 13 made offused glass, since the volume (particularly the thickness T) of thelight transmitting member 13 is large, it is possible to reduce theinfluence of the air bubbles.

Note that, as in a light detection device 1C illustrated in FIG. 6, aband pass filter 14 of a plate shape may be attached to a light emittingsurface 13 b of the light transmitting member 13 by an adhesive agent orother means. The band pass filter 14 of a plate shape is a lighttransmitting member made of, for example, silicon, glass, or othermaterials with a dielectric multilayer film formed on a surface thereof.The flatness of the light emitting surface 13 b is improved in the lighttransmitting member 13 made of fused glass since the thickness T islarge, and thus the band pass filter 14 can be suitably arranged on thelight emitting surface 13 b. According to the light detection device 1C,since the heat capacity is increased by the band pass filter 14 of aplate shape and the volume of the space in the package 2 is furtherreduced, the temperature inside the package 2 can be furtheruniformized. Furthermore, since the distance between the band passfilter 14 and the Fabry-Perot interference filter 10 is reduced by thethickness of the light transmitting member forming the band pass filter14 of a plate shape, it is further securely ensured that light incidenton the light transmission region 10 a of the Fabry-Perot interferencefilter 10 has been transmitted through the band pass filter 14.

In the light detection device 1C as well, like in the light detectiondevice 1A as described above, the light transmitting member 13 and theband pass filter 14 form a light transmitting unit 100. That is, thelight transmitting unit 100 includes the band pass filter 14 thattransmits light incident on the light transmission region 10 a of theFabry-Perot interference filter 10.

[Modifications]

Although the first embodiment and the second embodiment of the presentdisclosure have been described above, one embodiment of the presentdisclosure is not limited to the first embodiment or the secondembodiment described above. For example, the materials and the shapes ofthe respective configurations are not limited to the aforementionedmaterials or shapes but may employ various materials or shapes.

Moreover, the band pass filter 14 may be provided on the light incidentsurface 13 a of the light transmitting member 13 or may be provided onboth the light incident surface 13 a and the light emitting surface 13 bof the light transmitting member 13. As an example, as the lightdetection device 1B illustrated in FIG. 5, the band pass filter 14 maybe provided on the light incident surface 13 a of the light transmittingmember 13 which is substantially flush with the outer surface of the topwall 6 at the opening 2 a.

Furthermore, the Fabry-Perot interference filter 10 may not include thelaminated structure (the antireflection layer 41, the third laminatedbody 42, the intermediate layer 43, the fourth laminated body 44, thelight shielding layer 45, and the protective layer 46) provided on thelight emitting side surface 21 b of the substrate 21.

When viewed from a direction parallel to the line L, the outer edge ofthe light transmission region 10 a of the Fabry-Perot interferencefilter 10 may be positioned outside the outer edge of the opening 2 a.In this case, the ratio of light entering the light transmission region10 a out of light incident from the opening 2 a increases, and theutilization efficiency of light incident from the opening 2 a increases.Moreover, even if the position of the opening 2 a with respect to thelight transmission region 10 a is shifted to some extent, since lightincident from the opening 2 a enters the light transmission region 10 a,requirement of positional accuracy at the time of assembling the lightdetection devices 1A, 1B, and 1C is relaxed.

Third Embodiment [Configuration of Light Detection Device]

As illustrated in FIG. 7, a light detection device 1D includes a package2. The package 2 is a CAN package having a stem (second wall part) 3 anda cap 4. The cap 4 is integrally formed by a side wall (side wall part)5 and a top wall (first wall part) 6. The stem 3 and the cap 4 are madeof a metal material and are airtightly joined to each other. In thepackage 2 formed of a metal material, the side wall 5 has a cylindricalshape having a predetermined line L as a center line thereof. The stem 3and the top wall 6 face each other in a direction parallel to the line Land close each of both ends of the side wall 5.

On an inner surface 3 a of the stem 3, a wiring substrate 7 is fixed. Asa material of the wiring substrate 7, for example, silicon, ceramic,quartz, glass, plastic, or other materials can be used. On the wiringsubstrate 7, a temperature compensating element (not illustrated) suchas a light detector 8 and a thermistor is mounted. The light detector 8is arranged on the line L. More specifically, the light detector 8 isarranged such that the center line of a light receiving unit thereofcoincides with the line L. The light detector 8 is an infrared detectorsuch as a quantum type sensor using InGaAs or other compounds or athermal type sensor using a thermopile or a bolometer or otherinstruments. In a case where light of different wavelength regions ofultraviolet, visible, and near infrared regions, for example a siliconphotodiode or other components can be used as the light detector 8. Notethat the light detector 8 may include one light receiving unit or mayinclude a plurality of light receiving units in an arrayed shape.Furthermore, a plurality of light detectors 8 may be mounted on thewiring substrate 7.

On the wiring substrate 7, a plurality of spacers 9 are fixed. As amaterial of the spacers 9, for example, silicon, ceramic, quartz, glass,plastic, or other materials can be used. On the plurality of spacers 9,a Fabry-Perot interference filter 10 is fixed by, for example, anadhesive agent. The Fabry-Perot interference filter 10 is arranged onthe line L. More specifically, the Fabry-Perot interference filter 10 isarranged such that the center line of a light transmission region 10 acoincides with the line L. Note that the spacers 9 may be integrallyformed with the wiring substrate 7. The Fabry-Perot interference filter10 may be supported not by the plurality of spacers 9 but by one spacer9.

A plurality of lead pins 11 are fixed to the stem 3. More specifically,each of the lead pins 11 penetrates through the stem 3 in a state whereelectrical insulation and airtightness with the stem 3 is maintained.Electrode pads provided on the wiring substrate 7, terminals of thelight detector 8, terminals of the temperature compensating element, andterminals of the Fabry-Perot interference filter 10 are electricallyconnected to the respective lead pins 11 by wires 12. This enables inputand output of electric signals to and from each of the light detector 8,the temperature compensating element, and the Fabry-Perot interferencefilter 10.

An opening (light incident opening) 2 a is formed in the package 2. Morespecifically, the opening 2 a is formed in the top wall 6 of the cap 4such that the center line thereof coincides with the line L. When viewedfrom a direction parallel to the line L, the opening 2 a has circularshape. On an inner surface 6 a of the top wall 6, a light transmittingmember 13 is arranged so as to close the opening 2 a. The lighttransmitting member 13 is airtightly joined to the inner surface 6 a ofthe top wall 6. The light transmitting member 13 has a light incidentsurface 13 a and a light emitting surface (inner surface) 13 b facingeach other in a direction parallel to the line L and a side surface 13 cA light incident surface 13 a of the light transmitting member 13 issubstantially flush with an outer surface of a top wall 6 at the opening2 a. The side surface 13 c of the light transmitting member 13 is incontact with an inner surface 5 a of the side wall 5 of the package 2.That is, the light transmitting member 13 extends to the inside of theopening 2 a and the inner surface 5 a of the side wall 5. Such a lighttransmitting member 13 is formed by arranging a glass pellet inside acap 4 with the opening 2 a facing down and melting the glass pellet. Inother words, the light transmitting member 13 is formed of fused glass.

A band pass filter 14 is fixed to the light emitting surface 13 b of thelight transmitting member 13 by a bonding member 15. That is, thebonding member 15 fixes the band pass filter 14 on the inner surface 6 aof the top wall 6 via the light transmitting member 13 joined to theinner surface 6 a of the top wall 6. the band pass filter 14 selectivelytransmits light in a range of measurement wavelengths (light in apredetermined wavelength range and incident on the light transmissionregion 10 a of the Fabry-Perot interference filter 10) of the lightdetection device 1D out of light transmitted through the lighttransmitting member 13 (that is, only light in the wavelength range istransmitted). The band pass filter 14 has a rectangular plate shape.More specifically, the band pass filter 14 has a light incident surface14 a and a light emitting surface 14 b facing each other in a directionparallel to the line L and four side surfaces 14 c. The band pass filter14 is a light transmitting member formed into a rectangular plate shapefrom a light transmitting material (for example, silicon, glass, etc.)with a dielectric multilayer film (multilayer film formed by acombination of a high refractive material such as TiO₂ and Ta₂O₅ and alow refractive material such as SiO_(z) and MgF₂) formed thereon.

In the light detection device 1D, the light transmitting unit 100 isformed by the band pass filter 14. That is, the light transmitting unit100 includes the band pass filter 14 that transmits light incident onthe light transmission region 10 a of the Fabry-Perot interferencefilter 10.

The bonding member 15 has a first part 15 a arranged over the entireregion of the light incident surface 14 a of the band pass filter 14.That is, the first part 15 a is a part of the bonding member 15 arrangedbetween the light emitting surface 13 b of the light transmitting member13 and the light incident surface 14 a of the band pass filter 14 facingeach other. Furthermore, the bonding member 15 has a second part 15 bprotruding outward from the outer edge of the band pass filter 14 whenviewed from a direction parallel to the line L. The second part 15 bextends to the inner surface 5 a of the side wall 5 and is in contactwith the inner surface 5 a of the side wall 5. The second part 15 b isin contact with the side surfaces 14 c of the band pass filter 14. Asillustrated in FIG. 8, the thickness of the second part 15 b in adirection parallel to the line L is the maximum at a part in contactwith the central part of each of the side surfaces 14 c and is theminimum at a part in contact with each of the corner parts 14 d of theband pass filter 14 (corner parts formed by adjacent side surfaces 14c). However, in a case where the thickness of the second part 15 b inthe direction parallel to the line L is gradually reduced at each of thecorner parts 14 d than at the central part of each of the side surfaces14 c for example due to a convex curved surface of the second part 15 b,the thickness of the second part 15 b may not be the minimum at a partin contact with each of the corner parts 14 d. Occurrence of a crack ina corner part 14 d of the band pass filter 14 can be suppressed unlessthe thickness of the second part 15 b is maximized at a part in contactwith the respective corner parts 14 d. As a material of the bondingmember 15, a light transmitting material (for example, lighttransmitting resin, low melting point glass, etc.) can be used. Notethat, in FIG. 8, for convenience of explanation, only the package 2 andthe light transmitting member 13 are illustrated in cross section.

As illustrated in FIG. 7, in the light detection device 1D, the package2 accommodates the wiring substrate 7, the light detector 8, thetemperature compensating element (not illustrated), the plurality ofspacers 9, the Fabry-Perot interference filter 10, and the band passfilter 14. In the light detection device 1D, the opening 2 a, the lighttransmitting member 13, and the band pass filter 14 are arranged on oneside (second side) of the Fabry-Perot interference filter 10 on the lineL, and the light detector 8 is arranged on the other side (first side)of the Fabry-Perot interference filter 10 on the line L. Furthermore, inthe light detection device 1D, the stem 3 faces the top wall 6 of thecap 4 with the Fabry-Perot interference filter 10, the band pass filter14, and the light detector 8 interposed therebetween, and the side wall5 of the cap 4 surrounds the Fabry-Perot interference filter 10, theband pass filter 14, and light detector 8.

A thickness T of the light transmitting member 13 (thickness in adirection parallel to the line L, which is a distance between the lightincident surface 13 a and the light emitting surface 13 b) is greaterthan or equal to a value obtained by multiplying a distance D1 betweenthe Fabry-Perot interference filter 10 and the light transmitting member13 (distance between a surface of the Fabry-Perot interference filter 10on the light transmitting member 13 side and the light emitting surface13 b of the light transmitting member 13) by 0.3. Moreover, thethickness T of the light transmitting member 13 is greater than or equalto a distance D2 between the Fabry-Perot interference filter 10 and thelight detector 8 (distance between a surface of the Fabry-Perotinterference filter 10 on the light detector 8 side and a surface of thelight detector 8 on the Fabry-Perot interference filter 10 side).

The positional relationship and sizes of the respective components whenviewed from a direction parallel to the line L are as follows. Asillustrated in FIG. 9, the center line of the opening 2 a, the centerline of the light transmitting member 13, the center line of the bandpass filter 14, the center line of the light transmission region 10 a ofthe Fabry-Perot interference filter 10, and the center line of the lightreceiving unit of the light detector 8 coincides with the line L. Outeredges of the opening 2 a, the light transmitting member 13, the bondingmember 15, and the light transmission region 10 a of the Fabry-Perotinterference filter 10 have a circular shape. Outer edges of the bandpass filter 14, the Fabry-Perot interference filter 10, and the lightdetector 8 have a rectangular shape.

The outer edge of the light transmission region 10 a of the Fabry-Perotinterference filter 10 is positioned outside the outer edge of the lightdetector 8. The outer edge of the opening 2 a is positioned outside theouter edge of the light transmission region 10 a of the Fabry-Perotinterference filter 10. The outer edge of the Fabry-Perot interferencefilter 10 is positioned outside the outer edge of the opening 2 a. Theouter edge of the band pass filter 14 is positioned outside the outeredge of the Fabry-Perot interference filter 10. The outer edge of eachof the light transmitting member 13 and the bonding member 15 ispositioned outside the outer edge of the band pass filter 14 andcoincides with the inner surface 5 a of the side wall 5 of the cap 4.Note that “one outer edge is positioned outside another outer edge whenviewed from a predetermined direction” means that “the outer edgesurrounds the other outer edge when viewed from the predetermineddirection” or that “the outer edge includes the other outer edge whenviewed from the predetermined direction”.

In the light detection device 1D configured as described above, whenlight enters the band pass filter 14 from the outside via the opening 2a, the light transmitting member 13, and the bonding member 15, light ina predetermined wavelength range is selectively transmitted. When thelight transmitted through the band pass filter 14 is incident on thelight transmission region 10 a of the Fabry-Perot interference filter10, light having a predetermined wavelength out of light within thepredetermined wavelength range is selectively transmitted. The lighttransmitted through the light transmission region 10 a of theFabry-Perot interference filter 10 enters the light receiving unit ofthe light detector 8 and is detected by the light detector 8.

[Configuration of Fabry-Perot Interference Filter]

As illustrated in FIG. 10, in the Fabry-Perot interference filter 10, alight transmission region 10 a that transmits light corresponding to thedistance between a first mirror and a second mirror is included on theline L. In the light transmission region 10 a, the distance between thefirst mirror and the second mirror is controlled with an extremely highaccuracy. That is, in the Fabry-Perot interference filter 10, the lighttransmission region 10 a is a region in which the distance between thefirst mirror and the second mirror can be controlled to a predetermineddistance in order to selectively transmit light having a predeterminedwavelength and is a region through which light having a predeterminedwavelength corresponding to the distance between the first mirror andthe second mirror can be transmitted.

As illustrated in FIG. 11, the Fabry-Perot interference filter 10includes a substrate 21. On a surface 21 a of the substrate 21 on alight incident side, an antireflection layer 31, a first laminated body32, an intermediate layer 33, and a second laminated body 34 arelaminated in the order mentioned. A gap (air gap) S is formed betweenthe first laminated body 32 and the second laminated body 34 by theintermediate layer 33 of a frame shape. The substrate 21 is made of, forexample, silicon, quartz, glass, or other materials. In a case where thesubstrate 21 is made of silicon, the antireflection layer 31 and theintermediate layer 33 are made of; for example, silicon oxide. Thethickness of the intermediate layer 33 may be an integral multipleobtained by multiplying the central transmission wavelength (that is,the central wavelength of a wavelength range that the Fabry-Perotinterference filter 10 can transmit) by ½.

A part of the first laminated body 32 corresponding to the lighttransmission region 10 a functions as a first mirror 35. The firstmirror 35 is supported on the substrate 21 via the antireflection layer31. The first laminated body 32 includes a plurality of polysiliconlayers and a plurality of silicon nitride layers with each of theplurality of layers laminated alternately. The optical thickness of eachof the polysilicon layers and the silicon nitride layers forming thefirst mirror 35 may be an integral multiple obtained by multiplying thecentral transmission wavelength by ¼. Note that a silicon oxide layermay be used instead of the silicon nitride layer.

A part of the second laminated body 34 corresponding to the lighttransmission region 10 a functions as a second mirror 36 facing thefirst mirror 35 via the gap S. The second mirror 36 is supported on thesubstrate 21 via the antireflection layer 31, the first laminated body32, and the intermediate layer 33. The second laminated body 34 includesa plurality of polysilicon layers and a plurality of silicon nitridelayers with each of the plurality of layers laminated alternately. Theoptical thickness of each of the polysilicon layers and the siliconnitride layers forming the second mirror 36 may be an integral multipleobtained by multiplying the central transmission wavelength by ¼. Notethat a silicon oxide layer may be used instead of the silicon nitridelayer.

In a part of the second laminated body 34 corresponding to the gap S, aplurality of through holes 24 b extending from a surface 34 a of thesecond laminated body 34 to the gap S is included. The plurality ofthrough holes 24 b is formed to an extent that they do not substantiallyaffect the function of the second mirror 36. The plurality of throughholes 24 b have been used to form the gap S by removing a part of theintermediate layer 33 by etching.

In the first mirror 35, a first electrode 22 is formed so as to surroundthe light transmission region 10 s. In the first mirror 35, a secondelectrode 23 is formed so as to include the light transmission region 10a. The first electrode 22 and the second electrode 23 are formed bydoping the polysilicon layer with an impurity to reduce the resistance.The size of the second electrode 23 is substantially the same as thesize of the light transmission region 10 a.

On the second mirror 36, a third electrode 24 is formed. The thirdelectrode 24 faces the first electrode 22 and the second electrode 23via the gap S in a direction parallel to the line L. The third electrode24 is formed by doping the polysilicon layer with an impurity to reducethe resistance.

In the Fabry-Perot interference filter 10, the second electrode 23 ispositioned on the same plane as that of the first electrode 22 in adirection parallel to the line L. The distance between the secondelectrode 23 and the third electrode 24 is the same as the distancebetween the first electrode 22 and the third electrode 24. Furthermore,when viewed from a direction parallel to the line L, the secondelectrode 23 is surrounded by the first electrode 22.

A pair of terminals 25 are provided so as to face each other whileinterposing the light transmission region 10 a. Each of the terminals 25is arranged in a through hole extending from a surface 34 a of thesecond laminated body 34 to the first laminated body 32. Each of theterminals 25 is electrically connected to the first electrode 22 viawiring 22 a.

A pair of terminals 26 are provided so as to face each other whileinterposing the light transmission region 10 a. Each of the terminals 26is arranged in a through hole extending from the surface 34 a of thesecond laminated body 34 to a layer before the intermediate layer 33.Each of the terminals 26 is electrically connected to the secondelectrode 23 via wiring 23 a and is also electrically connected to thethird electrode 24 via wiring 24 a. Note that, a direction in which thepair of terminals 25 face each other and a direction in which the pairof terminals 26 face each other are perpendicular to each other (seeFIG. 10).

Trenches 27 and 28 are included on the surface 32 a of the firstlaminated body 32. The trench 27 extends annularly so as to surround aconnected part of the wiring 23 a, with the terminal 26, extending fromthe terminal 26 along the direction parallel to the line L. The trench27 electrically insulates the first electrode 22 from the wiring 23 a. Atrench 28 annularly extends along the inner edge of the first electrode22. The trench 28 electrically insulates the first electrode 22 from thesecond electrode 23. Regions inside the trenches 27 and 28 may be madeof an insulating material or void.

Trenches 29 are included on the surface 34 a of the second laminatedbody 34. A trench 29 annularly extends so as to surround a terminal 25.The trench 29 electrically insulates the terminal 25 from the thirdelectrode 24. A region inside the trench 28 may be made of an insulatingmaterial or void.

On a surface 21 b of the substrate 21 on a light emitting side, anantireflection layer 41, a third laminated body 42, an intermediatelayer 43, and a fourth laminated body 44 are laminated in the ordermentioned. The antireflection layer 41 and the intermediate layer 43have a similar configuration to those of the antireflection layer 31 andthe intermediate layer 33, respectively. The third laminated body 42 andthe fourth laminated body 44 have lamination configurations symmetricalto those of the first laminated body 32 and the second laminated body34, respectively, with respect to the substrate 21. The antireflectionlayer 41, the third laminated body 42, the intermediate layer 43, andthe fourth laminated body 44 have a function of suppressing warping ofthe substrate 21.

The antireflection layer 41, the third laminated body 42, theintermediate layer 43, and the fourth laminated body 44 include anopening 40 a so as to include the light transmission region 10 a. Theopening 40 a has substantially the same diameter as the size of thelight transmission region 10 a. The opening 40 a is open on the lightemitting side while a bottom surface of the opening 40 a reaches theantireflection layer 41. A light shielding layer 45 is formed on asurface of the fourth laminated body 44 on the light emitting side. Thelight shielding layer 45 is made of, for example, aluminum. A protectivelayer 46 is formed on a surface of the light shielding layer 45 and aninner surface of the opening 40 a. The protective layer 46 is made of,for example, aluminum oxide. Note that, by setting the thickness of theprotective layer 46 at 1 to 100 nm (preferably, about 30 nm), opticalinfluence by the protective layer 46 can be negligible.

In the Fabry-Perot interference filter 10 configured in the abovemanner, when a voltage is applied between the first electrode 22 and thethird electrode 24 via the respective terminals 25 and 26, electrostaticforce corresponding to the voltage is generated between the firstelectrode 22 and the third electrode 24. Due to the electrostatic force,the second mirror 36 is attracted to the side of the first mirror 35fixed to the substrate 21, and the distance between the first mirror 35and the second mirror 36 is adjusted. As described above, in theFabry-Perot interference filter 10, the distance between the firstmirror 35 and the second mirror 36 is allowed to be variable.

The wavelength of light transmitted through the Fabry-Perot interferencefilter 10 depends on the distance between the first mirror 35 and thesecond mirror 36 in the light transmission region 10 a. Therefore, byadjusting the voltage applied between the first electrode 22 and thethird electrode 24, a wavelength of transmitted light can be selected asappropriate. At this time, the second electrode 23 has the samepotential as that of the third electrode 24. Therefore, the secondelectrode 23 functions as a compensation electrode for keeping the firstmirror 35 and the second mirror 36 flat in the light transmission region10 a.

The light detection device 1D can obtain an optical spectrum bydetecting light transmitted through the light transmission region 10 aof the Fabry-Perot interference filter 10 by the light detector 8 whilechanging the voltage applied to the Fabry-Perot interference filter 10(that is, changing the distance between the first mirror 35 and thesecond mirror 36 in the Fabry-Perot interference filter 10).

[Actions and Effects]

As described above, in the light detection device 1D, the side wall 5 ofthe package 2 has a cylindrical shape while the band pass filter 14 hasa rectangular plate shape. As a result, the distance between each of thecorner parts 14 d of the band pass filter 14 and the inner surface 5 aof the side wall 5 becomes smaller than the distance between each of theside surfaces 14 c of the band pass filter 14 and the inner surface 5 aof the side wall 5. Therefore, the band pass filter 14 fixed on theinner surface 6 a of the top wall 6 of the package 2 is positioned byeach of the corner parts 14 d thereof with a high accuracy. Here, forexample in a case where the band pass filter 14 has a circular plateshape, if the diameter of the band pass filter 14 is increased such thatthe distance between a side surface 14 c of the band pass filter 14 andthe inner surface 5 a of a side wall 5 becomes smaller in order toimplement high-precision positioning of the band pass filter 14, thefollowing problem occurs. That is, since an area of the light incidentsurface 14 a of the band pass filter 14 thermally connected to the innersurface 6 a of the top wall 6 of the package 2 is increased, the bandpass filter 14 is easily affected by heat (deformation or otherdisadvantages due to heat) from the package 2. On the other hand, if theband pass filter 14 has a rectangular plate shape, an area of the lightincident surface 14 a of the band pass filter 14 thermally connected tothe inner surface 6 a of the top wall 6 of the package 2 becomessmaller, for example as compared to the case where the band pass filter14 has a circular plate shape, and thus the band pass filter 14 is lesslikely to be affected by heat from the package 2. Furthermore, since theouter edge of the Fabry-Perot interference filter 10 is positionedoutside the outer edge of the opening 2 a and the outer edge of the bandpass filter 14 is positioned outside the outer edge of the Fabry-Perotinterference filter 10, it is ensured that light incident on the lighttransmission region 10 a of the Fabry-Perot interference filter 10 hasbeen transmitted through the band pass filter 14. As described above,according to the light detection device 1D, the band pass filter 14 canfunction properly.

Here, the importance of allowing the band pass filter 14 toappropriately function in the light detection device 1D including theFabry-Perot interference filter 10 will be described. In the Fabry-Perotinterference filter 10, a wavelength λ that satisfies λ=2nd/a (n:refractive index, d: distance between the first mirror 35 and the secondmirror 36, a: integer) is a peak wavelength of the light transmittedthrough the light transmission region 10 a. Even with the same distanced, if a value of the integer a is increased (brought to a higher orderside), a peak wavelength corresponding thereto appears on a shorterwavelength side. Therefore, in the light detection device 1D, inaddition to the Fabry-Perot interference filter 10, the band pass filter14 that cuts off light (especially light on the short wavelength side)outside a predetermined wavelength range is required.

For example, in a light detection device for obtaining an opticalspectrum of second-order light (a=2), it is necessary to cut offmulti-order light of an order higher than or equal to three appearingparticularly on the shorter wavelength side. Furthermore, a case isassumed where an InGaAs PIN photodiode (single element photodiode) isused in the light detector 8 and reasonable white light (halogen lampetc.) is used as a light source. Therefore, it is necessary to arrangethe band pass filter 14 at a position on the optical axis of the lightsource/light detector 8. When the light detection device including theband pass filter 14 and the light detection device not including theband pass filter 14 are compared, it is confirmed that in the lightdetection device including the band pass filter 14, high order light onthe shorter wavelength side has cut off.

As described above, since the light detection device 1D includes theband pass filter 14, it is possible to provide the light detectiondevice 1D as a general product with high completeness which does notrequire customization of the Fabry-Perot interference filter 10.Furthermore, since a single element photodiode can be used as the lightdetector 8, the manufacturing cost of the light detection device 1D canbe reduced.

Next, advantages of the cylindrical shape of the side wall 5 of thepackage 2 will be described. First, in the light detection device 1D,since the side wall 5 of the package 2 has a cylindrical shape,durability of the light detection device 1D is improved. Morespecifically, since the side wall 5 of the package 2 has a cylindricalshape, stability of the shape of the package 2 is higher than, forexample, the case where the side wall 5 of the package 2 has a polygonalcylindrical shape.

Moreover, in the light detection device 1D, since the side wall 5 of thepackage 2 has a cylindrical shape, stress is unlikely to be concentratedfor example as compared with the case where the package 2 has apolygonal shape. This is because stress due to an impact is notconcentrated on one point but is dispersed in the case where the sidewall 5 of the package 2 has a cylindrical shape contrary to the casewhere the package 2 has a polygonal tubular shape, and stress due to animpact applied to the package 2 is likely to concentrate on the cornerparts. In particular, the Fabry-Perot interference filter 10accommodated in the package 2 is vulnerable to a physical impact.Therefore, by allowing the side wall 5 of the package 2 to have acylindrical shape, the Fabry-Perot interference filter 10 is suitablyprotected from an external physical impact.

Moreover, there are cases where a thermal stress is generated in thepackage 2 depending on thermal history at the time of assembling thelight detection device 1D (thermally curing the bonding member 15,connecting the wires 12, sealing by the stem 3, etc.), temperaturechange after assembling, or other reasons. The thermal stress isgenerated by a difference in coefficient of linear thermal expansionamong the members forming the light detection device 1D. It is desirableto avoid that this thermal stress is concentrated and accumulated in aspecific location or in a specific direction in the light detectiondevice 1D. This is because if a thermal stress concentrates in aspecific location or in a specific direction, this leads tocharacteristic abnormality or breakage of the light detection device 1D.In the light detection device 1D, since the side wall 5 of the package 2has a cylindrical shape, a generated thermal stress is dispersed withoutconcentrating on one point. As a result, occurrence of characteristicabnormality in the light detection device 1D or breakage of the lightdetection device 1D can be suppressed.

The light detection device 1D further includes the light transmittingmember 13 arranged on the inner surface 6 a of the top wall 6 so as toclose the opening 2 a, in which the band pass filter 14 is fixed to thelight emitting surface (inner surface) 13 b of the light transmittingmember 13 by the bonding member 15, and the bonding member 15 isarranged over the entire region of the light incident surface 14 a ofthe band pass filter 14 facing the light emitting surface 13 b of thelight transmitting member 13. According to this configuration, since thebonding member 15 is arranged over the entire region of the lightincident surface 14 a of the band pass filter 14, the band pass filter14 is securely fixed to the inner surface 6 a of the top wall 6.Furthermore, even if air bubbles are generated in the bonding member 15at the time of manufacturing, the air bubbles easily escape from betweenthe side surfaces 14 c of the band pass filter 14 and the inner surface5 a of the side wall 5, scattering, diffraction, and the like at thebonding member 15 are suppressed. Furthermore, according to thisconfiguration, since the light transmitting member 13 is provided,airtightness of the package 2 is improved. Furthermore, since the bandpass filter 14 is fixed to the light emitting surface 13 b of the lighttransmitting member 13, thermal influence from the package 2 is unlikelyto be received. Furthermore, since the band pass filter 14 is fixed tothe light emitting surface 13 b of the light transmitting member 13,occurrence of a damage, such as a scratch, to the band pass filter 14due to physical interference from the opening 2 a can be prevented.

Here, the effect of suppressing scattering and diffraction of light andthe like at the bonding member 15 will be described. There are caseswhere the light emitting surface 13 b of the light transmitting member13 does not have good flatness and have a curvature. In particular,there are cases where a region of the light emitting surface 13 b of thelight transmitting member 13 facing the opening 2 a is distorted so asto be recessed toward the opening 2 a. This is because in this regionthe light transmitting member 13 is distorted so as to be recessedtoward the opening 2 a due to the weight of the light transmittingmember 13 (which is molten glass) at the time of firing. As a result, itbecomes difficult for air bubbles generated in the bonding member 15 atthe time of manufacturing to escape from a region of the light emittingsurface 13 b of the light transmitting member 13 facing the opening 2 a,which may disadvantageously cause scattering, unwanted diffraction, andthe like of light at the bonding member 15. Furthermore, there are caseswhere the flatness of the light incident surface 14 a of the band passfilter 14 is not good. As a result, disadvantageously, the band passfilter 14 may not be positioned with a high accuracy.

Furthermore, in the light detection device 1D, each of the corner parts14 d of the band pass filter 14 and the inner surface 5 a of the sidewall 5 are not in contact with each other but are separated from eachother. This can prevent breakage of the band pass filter 14 (inparticular, each of the corner parts 14 d) due to a contact between eachof the corner parts 14 d and the inner surface 5 a of the side wall 5.Furthermore, since each of the corner parts 14 d of the band pass filter14 and the inner surface 5 a of the side wall 5 are not in contact witheach other but are separated from each other, the band pass filter 14 isless likely to be affected by heat from the package 2. Furthermore,since each of the corner parts 14 d of the band pass filter 14 and theinner surface 5 a of the side wall 5 are not in contact with each otherbut are separated from each other, that is, since each of the cornerparts 14 d of the band pass filter 14 is separated from an R unit (Runit formed by the light emitting surface 13 b of the light transmittingmember 13 and the inner surface 5 a of the side wall 5) of the package2, the band pass filter 14 is securely fixed to the light emittingsurface 13 b of the light transmitting member 13 which is a flatsurface.

In the light detection device 1D, the side wall 5 of the package 2 has acylindrical shape while the band pass filter 14 has a rectangular plateshape. As a result, the band pass filter 14 is positioned by each of thecorner parts 14 d thereof with a high accuracy as described above. Here,for example in a case where the band pass filter 14 has a circular plateshape, if the diameter of the band pass filter 14 is increased such thatthe distance between a side surface 14 c of the band pass filter 14 andthe inner surface 5 a of a side wall 5 becomes smaller in order toimplement high-precision positioning of the band pass filter 14, thefollowing problem occurs. That is, since the area of the light incidentsurface 14 a of the band pass filter 14 fixed to the light emittingsurface 13 b of the light transmitting member 13 is increased by thebonding member 15, it is becomes difficult for air bubbles generated inthe bonding member 15 to be removed therefrom. On the other hand, whenthe band pass filter 14 has a rectangular plate shape, the area of thelight incident surface 14 a of the band pass filter 14 fixed on thelight emitting surface 13 b of the light transmitting member 13 becomessmaller as compared to the case where for example the band pass filter14 has a circular plate shape, which facilitates bubbles generated inthe bonding member 15 to escape from between the side surfaces 14 c ofthe band pass filter 14 and the inner surface 5 a of the side wall 5. Asa result, scattering and diffraction of light and the like at thebonding member 15 are suppressed.

Note that if the region of the light emitting surface 13 b of the lighttransmitting member 13 facing the opening 2 a is distorted so as to berecessed toward the opening 2 a, it is avoided that a region of thelight incident surface 14 a of the band pass filter 14 where lightenters is physically brought into contact with the light emittingsurface 13 b of the light transmitting member 13, which can preventoccurrence of a damaged in the region.

Moreover, in the light detection device 1D, the bonding member 15protrudes outward from the outer edge of the band pass filter 14 whenviewed from a direction parallel to the line L, and a part of thebonding member 15 protruding outward from the outer edge of the bandpass filter 14 is in contact with side surfaces 14 c of the band passfilter 14. According to this configuration, the band pass filter 14 ismore securely fixed.

In the light detection device 1D, the thickness of the second part 15 bof the bonding member 15 in the direction parallel to the line L is themaximum at a part in contact with the central part of each of the sidesurfaces 14 c and is the minimum at a part in contact with each of thecorner parts 14 d of the band pass filter 14. According to thisconfiguration, for example at the time of curing the bonding member 15,it is possible to suppress occurrence of a crack in the bonding member15 at parts corresponding to the corner parts 144 of the band passfilter 14. However, in a case where the thickness of the second part 15b in the direction parallel to the line L is gradually reduced at eachof the corner parts 14 d than at the central part of each of the sidesurfaces 14 c for example due to a convex curved surface of the secondpart 15 b, the thickness of the second part 15 b may not be the minimumat a part in contact with each of the corner parts 14 d. Occurrence of acrack in a corner part 14 d of the band pass filter 14 can be suppressedunless the thickness of the second part 15 b is maximized at a part incontact with the respective corner parts 14 d.

Furthermore, in the light detection device 1D, the opening 2 a has acircular shape when viewed from a direction parallel to the line L.According to this configuration, the intensity profile of light incidenton the package 2 is uniformized.

Moreover, in the light detection device 1D, the band pass filter 14 hasa rectangular plate shape. According to this configuration, it ispossible to effectively suppress the thermal influence given to the bandpass filter 14 from the package 2 while the stability in fixing of theband pass filter 14 on the inner surface 6 a of the top wall 6 of thepackage 2 is ensured. Furthermore, it becomes further easier for airbubbles generated in the bonding member 15 at the time of manufacturingto escape from between the side surfaces 14 c of the band pass filter 14and the inner surface 5 a of the side wall 5 of the package 2, and thusscattering and diffraction of light and the like at the bonding member15 are suppressed. Furthermore, the manufacturing cost of the band passfilter 14 by wafer processing is reduced.

In the light detection device 1D, the package 2 is formed of a metalmaterial. Since hermetic sealing is possible according to thisconfiguration, airtightness of the package 2 is improved for example ascompared with a package 2 formed of plastic. As a result, processing forcountermeasures against humidity of each component accommodated insidethe package 2 becomes unnecessary, and the manufacturing cost of thelight detection device 1D is reduced. Furthermore, if the package 2 isformed of a metal material, the strength of the package 2 is improved ascompared to a package 2 formed of, for example, plastic, and thus eachcomponent accommodated inside the package 2 protected from externalphysical impact. Furthermore, if the package 2 is formed of a metalmaterial, electrical shielding is facilitated. Note that in the casewhere the package 2 is formed of a metal material, the thermalconductivity of the package 2 is increased. However as described above,since the side wall 5 of the package 2 has a cylindrical shape while theband pass filter 14 has a rectangular plate shape, the band pass filter14 is unlikely to be affected by heat from the package 2.

In contrast, in the light detection device 1D, the outer edge of theFabry-Perot interference filter 10 is positioned outside the outer edgeof the opening 2 a of the package 2, and the outer edge of the lighttransmitting member 13 is positioned outside the outer edge of theFabry-Perot interference filter 10. This can prevent light from enteringthe package 2 via the side surfaces 13 c of the light transmittingmember 13 due to an incident angle of light at the opening 2 a,diffraction at the opening 2 a, etc. and becoming stray light. This canfurther prevent light, which has become stray light due to an incidentangle of light at the opening 2 a, diffraction at the opening 2 a, etc.,from entering the light detector 8.

The prevention of stray light from entering the light detector 8 will bedescribed in more detail. A part of light entering the opening 2 a ofthe package 2 may be emitted from the side surfaces 13 c of the lighttransmitting member 13 into the package 2 due to an incident angle oflight at the opening 2 a, diffraction at the side surface of the opening2 a and at an emitting side corner (corner where the side surface of theopening 2 a meets the inner surface 6 a of the top wall 6), etc. Whensuch light is multiple-reflected within the package 2 and enters thelight detector 8, this appears as noise due to stray light in an outputsignal, which leads to degradation of light detecting characteristics.In particular, since the side surfaces 13 c of the light transmittingmember 13 are often rougher than the light incident surface 13 a and thelight emitting surface 13 b of the light transmitting member 13 in manycases, light emitted from the side surfaces 13 c of the lighttransmitting member 13 into the package 2 is likely to be scattered andto enter the light detector 8. Contrary, in the light detection device1D, the outer edge of the Fabry-Perot interference filter 10 ispositioned outside the outer edge of the opening 2 a of the package 2,and the outer edge of the light transmitting member 13 is positionedoutside the outer edge of the Fabry-Perot interference filter 10.Moreover, the outer edge of the light transmitting member 13, that is,the side surface 13 c of the light transmitting member 13 is in contactwith the inner surface 5 a of the side wall 5 of the package 2. As aresult, for example as compared with the case where the outer edge ofthe light transmitting member 13 is positioned inside the outer edge ofthe Fabry-Perot interference filter 10, the side surfaces 13 c of thelight transmitting member 13 are positioned apart from the lighttransmission region 10 a of the Fabry-Perot interference filter 10 andthe light detector 8. Moreover, the side surface 13 c of the lighttransmitting member 13 is in contact with the inner surface 5 a of theside wall 5 of the package 2 and is covered by the inner surface 5 a.Therefore, the incidence of stray light on the light detector 8 issuppressed, and the S/N ratio and the resolution are improved.

Furthermore in the light detection device 1D, an outer edge of the lighttransmission region 10 a of the Fabry-Perot interference filter 10 ispositioned outside an outer edge of the light detector 8. The outer edgeof the opening 2 a is positioned outside the outer edge of the lighttransmission region 10 a of the Fabry-Perot interference filter 10. Theouter edge of the Fabry-Perot interference filter 10 is positionedoutside the outer edge of the opening 2 a. The outer edge of the bandpass filter 14 is positioned outside the outer edge of the Fabry-Perotinterference filter 10. As a result, it is ensured that light incidenton the light detector 8 via the opening 2 a and the light transmissionregion 10 a of the Fabry-Perot interference filter 10 has beentransmitted by the band pass filter 14.

Furthermore in the light detection device 1D, an outer edge of theFabry-Perot interference filter 10 is positioned outside an outer edgeof the light detector 8. This can prevent light not transmitted by thelight transmission region 10 a of the Fabry-Perot interference filter 10from entering the light detector 8 as stray light.

Moreover, the light detection device 1D includes the light transmittingmember 13. In the light detection device 1D, the thickness T of thelight transmitting member 13 is a value larger than or equal to a valueobtained by multiplying the distance D1 between the Fabry-Perotinterference filter 10 and the light transmitting member 13 by 0.3. As aresult, since the heat capacity of the light transmitting member 13 isincreased while the volume of the space in the package 2 is reduced, thetemperature in the package 2 can be uniformized. Therefore, each unitaccommodated in the package 2 such as the band pass filter 14 and theFabry-Perot interference filter 10 is less likely to be affected by atemperature change. Furthermore, since the light transmitting member 13moves relatively closer to the Fabry-Perot interference filter 10, thiscan prevent light not transmitted by the light transmission region 10 aof the Fabry-Perot interference filter 10 from entering the lightdetector 8 as stray light. Note that, in order to uniformize thetemperature in the package 2 and to further suppress incidence of straylight on the light detector 8, it is preferable that the thickness T isa value larger than or equal to a value obtained by multiplying thedistance D1 by 0.6.

Moreover, in the light detection device 1D, the thickness T of the lighttransmitting member 13 is a value larger than or equal to the distanceD2 between the Fabry-Perot interference filter 10 and the light detector8. As a result, since the heat capacity of the light transmitting member13 is increased while the volume of the space in the package 2 isreduced, the temperature in the package 2 can be further uniformized.

In the light detection device 1D, the terminals 25 and 26 of theFabry-Perot interference filter 10 and the lead pins 11 are electricallyconnected by wires 12. As described above, in the light detection device1D, the outer edge of the Fabry-Perot interference filter 10 ispositioned outside the outer edge of the opening 2 a of the package 2,and the outer edge of the light transmitting member 13 is positionedoutside the outer edge of the Fabry-Perot interference filter 10.Moreover, the outer edge of the light transmitting member 13, that is,the side surface 13 c of the light transmitting member 13 is in contactwith the inner surface 5 a of the side wall 5 of the package 2. In otherwords, the light transmitting member 13 covers the entire inner surface6 a of the top wall 6 of the package 2. Therefore, even if the wires 12bend, contact between the wires 12 and the inner surface 6 a of the topwall 6 of the package 2 can be prevented.

Prevention of contact between the wires 12 and the package 2 will bedescribed more specifically. When a wire 12 is brought into contact withthe package 2 made of metal, an electric signal for controlling theFabry-Perot interference filter 10 also flows in the package 2, whichmakes it difficult to control the Fabry-Perot interference filter 10.Contrary to this, even when a wire 12 is brought into contact with thelight transmitting member 13 made of an insulating material, an electricsignal for controlling the Fabry-Perot interference filter 10 does notflow in the light transmitting member 13, and thus the Fabry-Perotinterference filter 10 can be controlled with a high accuracy. The aboveconfiguration that can prevent contact between the wires 12 and thepackage 2 is important.

Furthermore, in the light detection device 1D, a silicon substrate isadopted as the substrate 21 of the Fabry-Perot interference filter 10,and an InGaAs substrate formed with a photoelectric conversion region isadopted as the light detector 8, whereby the following actions andeffects are achieved. The light detector 8 having the InGaAs substrateformed with the photoelectric conversion region has a high sensitivityto light having a wavelength within a range between 1200 nm and 2100 nm,for example, as compared to light having a wavelength shorter than 1200nm and light having a wavelength longer than 2100 nm. However, the lightdetector 8 has a high sensitivity to light having a wavelength shorterthan 1200 nm as compared with light having a wavelength longer than 2100nm. Meanwhile, the silicon substrate has a higher absorptivity to lighthaving a wavelength shorter than 1200 nm as compared with light having awavelength of 1200 nm or more (although this depends on a manufacturingmethod, the thickness, and an impurity concentration of the siliconsubstrate, a high absorptivity is exhibited especially for light havinga wavelength shorter than 1100 nm). Therefore, with the aboveconfiguration, for example in a case where light having a wavelengthwithin the range between 1200 nm and 2100 nm should be detected, thesilicon substrate of the Fabry-Perot interference filter 10 can becaused to function as a high-pass filter. As a result, it is possible tosecurely suppress detection of noise light (light having a wavelengthshorter than 1200 nm (in particular, shorter than 1100 nm) and lighthaving a wavelength longer than 2100 nm) by the light detector 8 by thesynergistic effect with the band pass filter 14.

In contrast, in the light detection device 1D, the outer edge of theFabry-Perot interference filter 10 of a chip shape is positioned outsidethe outer edge of the opening 2 a of the package 2, and the outer edgeof the light transmitting unit 100 is positioned outside the outer edgeof the Fabry-Perot interference filter 10. This can prevent light fromentering the package 2 via the side surface of the light transmittingunit 100 due to an incident angle of light at the opening 2 a,diffraction at the opening 2 a, etc. and becoming stray light. This canfurther prevent light, which has become stray light due to an incidentangle of light at the opening 2 a, diffraction at the opening 2 a, etc.,from entering the light detector 8. Furthermore, for example as comparedto a case where the outer edge of the light transmitting unit 100 ispositioned inside the outer edge of the Fabry-Perot interference filter10, the heat capacity of the light transmitting unit 100 and a thermallyconnected area between the light transmitting unit 100 and the package 2increases, and thus as a result the temperature in the package 2 can beuniformized. As described above, light detecting characteristics areimproved in the light detection device 1D.

Fourth Embodiment [Configuration of Light Detection Device]

As illustrated in FIGS. 12 and 13, a light detection device 1E isdifferent from the light detection device 1D described above mainly inthe point that a bonding member 15 is arranged so as to correspond toeach corner part (corner part formed by adjacent side surfaces 14 c) ofthe band pass filter 14.

In the light detection device 1E, at each of the corner parts of theband pass filter 14, a first part 15 a of the bonding member 15 isarranged at a corner region 14 e out of a light incident surface 14 a ofthe band pass filter 14 (out of the light incident surface 14 a, aregion including a corner part formed by adjacent side surfaces 14 c).That is, the first part 15 a is arranged between the light emittingsurface 13 b of the light transmitting member 13 and the corner regions14 e of the band pass filter 14 facing each other. In each of the cornerparts of the band pass filter 14, a second part 15 b of the bondingmember 15S protrudes outward from the outer edge of the band pass filter14 when viewed from a direction parallel to the line L. The second part15 b extends to the inner surface 5 a of the side wall 5 and is incontact with the inner surface 5 a of the side wall 5. The second part15 b is in contact with the side surfaces 14 c of the band pass filter14. The second part 15 b covers regions of the light emitting surface 14b of the band pass filter 14 that face the corner regions 14 e. As aresult, the band pass filter 14 is more securely fixed. At this time,since the corner regions 14 e of the band pass filter 14 are positionedso as to be farthest from the opening 2 a, there is a low possibilitythat the second parts 15 b covering regions of the light emittingsurface 14 b facing the corner regions 14 e cover a region of the lightemitting surface 14 b facing the light transmission region 10 a.Moreover, the bonding members 15 at the respective corner parts of theband pass filter 14 are separated from each other. As described above,in the light detection device 1E, the bonding members 15 are notarranged at a region of the light incident surface 14 a of the band passfilter 14 excluding the corner regions 14 e but is arranged at thecorner regions 14 e. Note that also in the light detection device 1E,the bonding members 15 fix the band pass filter 14 on the inner surface6 a of the top wall 6 via the light transmitting member 13 joined to theinner surface 6 a of the top wall 6.

Also in the light detection device 1E, like in the light detectiondevice 1D as described above, the band pass filter 14 forms a lighttransmitting unit 100. That is, the light transmitting unit 100 includesthe band pass filter 14 that transmits light incident on the lighttransmission region 10 a of the Fabry-Perot interference filter 10.

Note that if the region of the light emitting surface 13 b of the lighttransmitting member 13 facing the opening 2 a is distorted so as to berecessed toward the opening 2 a, it is avoided that a region of thelight incident surface 14 a of the band pass filter 14 where lightenters is physically brought into contact with the light emittingsurface 13 b of the light transmitting member 13, which can preventoccurrence of a damaged in the region. Furthermore, it is possible toprevent the bonding members 15 arranged so as to correspond to therespective corner parts of the band pass filter 14 from entering theregion of the light emitting surface 13 b of the light transmittingmember 13 facing the opening 2 a. This is because a region surroundingthe region of the light emitting surface 13 b of the light transmittingmember 13 facing the opening 2 a tends to swell.

[Actions and Effects]

As described above, according to the light detection device 1E, the bandpass filter 14 can be caused to function properly like the lightdetection device 1D described above. Moreover, in the light detectiondevice 1E, like the light detection device 1D described above, lightdetecting characteristics are improved.

The light detection device 1E further includes the light transmittingmember 13 arranged on the inner surface 6 a of the top wall 6 so as toclose the opening 2 a, in which the band pass filter 14 is fixed to thelight emitting surface 13 b of the light transmitting member 13 by thebonding member 15, and the bonding members 15 are not arranged at aregion of the light incident surface 14 a of the band pass filter 14excluding the corner regions 14 e facing the light emitting surface 13 bof the light transmitting member 13 but is arranged at the cornerregions 14 e. According to this configuration, since the bonding member15 is not arranged in a region of the light incident surface 14 a of theband pass filter 14 excluding the corner regions 14 e, scattering anddiffraction of light and the like at the bonding member 15 are moresecurely suppressed. Furthermore, according to this configuration, sincethe light transmitting member 13 is provided, airtightness of thepackage 2 is improved. Furthermore, since the band pass filter 14 isfixed to the light emitting surface 13 b of the light transmittingmember 13, thermal influence from the package 2 is unlikely to bereceived.

Furthermore, since the bonding members 15 are not arranged at the regionof the light incident surface 14 a of the band pass filter 14 excludingthe corner regions 14 e, the usage amount of the bonding members 15 isreduced. This reduces the amount of outgas remaining in the package 2and reduces the amount of outgas adhered to the Fabry-Perot interferencefilter 10 and a light receiving surfaces of the light detector 8.Therefore, the Fabry-Perot interference filter 10 and the light detector8 are unlikely to be subjected to a change in and deterioration of lightdetecting characteristics and the like.

Fifth Embodiment [Configuration of Light Detection Device]

As illustrated in FIGS. 14 and 15, a light detection device 1F is mainlydifferent from the light detection device 1D described above in that thelight transmitting member 13 is not included.

In the light detection device 1F, a band pass filter 14 is directlyfixed to an inner surface 6 a of a top wall 6 by a bonding member 15.That is, in the light detection device 1F, the bonding member 15 fixesthe band pass filter 14 on the inner surface 6 a of the top wall 6without interposing another member (such as the light transmittingmember 13 joined to the inner surface 6 a of the top wall 6). A firstpart 15 a of the bonding member 15 is arranged at a region of a lightincident surface 14 a of the band pass filter 14 facing the innersurface 6 a of the top wall 6 excluding an opposed region 14 f facingthe opening 2 a. That is, the first part 15 a is arranged between theinner surface 6 a of the top wall 6 and the region (that is, the regionof the light incident surface 14 a of the band pass filter 14 excludingthe opposed region 14 t) facing each other. A second part 15 b of thebonding member 15 protrudes outward from the outer edge of the band passfilter 14 when viewed from a direction parallel to the line L. Thesecond part 15 b extends to the inner surface 5 a of the side wall 5 andis in contact with the inner surface 5 a of the side wall 5. The secondpart 15 b is in contact with the side surfaces 14 c of the band passfilter 14.

Also in the light detection device 1F, like in the light detectiondevice 1D as described above, the band pass filter 14 forms a lighttransmitting unit 100. That is, the light transmitting unit 100 includesthe band pass filter 14 that transmits light incident on the lighttransmission region 10 a of the Fabry-Perot interference filter 10.

[Actions and Effects]

As described above, according to the light detection device 1F, the bandpass filter 14 can be caused to function properly like the lightdetection device 1D described above. Moreover, in the light detectiondevice 1F, like the light detection device 1D described above, lightdetecting characteristics are improved.

Furthermore, in the light detection device 1F, the band pass filter 14is fixed to the inner surface 6 a of the top wall 6 by the bondingmember 15, and the bonding member 15 is arranged at a region of thelight incident surface 14 a of the band pass filter 14 facing the innersurface 6 a of the top wall 6 excluding the opposed region 14 f facingto the opening 2 a. According to this configuration, since the bondingmember 15 is arranged in the region of the light incident surface 14 aof the band pass filter 14 other than the opposed region 14 f facing theopening 2 a, the band pass filter 14 is securely fixed on the innersurface 6 a of the top wall 6. Furthermore, even if air bubbles aregenerated in the bonding member 15 at the time of manufacturing, the airbubbles easily escape not only from between the side surfaces 14 c ofthe band pass filter 14 and the inner surface 5 a of the side wall 5 butalso from the opening 2 a, scattering and diffraction of light and thelike at the bonding member 15 are suppressed.

Sixth Embodiment [Configuration of Light Detection Device]

As illustrated in FIGS. 16 and 17, a light detection device 10 is mainlydifferent from the light detection device 1E described above in that thelight transmitting member 13 is not included.

In the light detection device 1G, a band pass filter 14 is directlyfixed to an inner surface 6 a of a top wall 6 by bonding members 15.That is, in the light detection device 1G, the bonding members 15 fixthe band pass filter 14 on the inner surface 6 a of the top wall 6without interposing another member (such as the light transmittingmember 13 joined to the inner surface 6 a of the top wall 6). In eachcorner part of the band pass filter 14, a first part 15 a of a bondingmember 15 is arranged at a corner region 14 e of a light incidentsurface 14 a of the band pass filter 14. That is, the first part 15 a isarranged between the inner surface 6 a of the top wall 6 and the cornerregions 14 of the band pass filter 14 facing each other. In each of thecorner parts of the band pass filter 14, a second part 15 b of thebonding member 15 protrudes outward from the outer edge of the band passfilter 14 when viewed from a direction parallel to the line L. Thesecond part 15 b extends to the inner surface 5 a of the side wall 5 andis in contact with the inner surface 5 a of the side wall 5. The secondpart 5 b is in contact with the side surfaces 14 c of the band passfilter 14. The second part 15 b covers regions of the light emittingsurface 14 b of the band pass filter 14 that face the corner regions 14e. As a result, the band pass filter 14 is more securely fixed. At thistime, since the corner regions 14 e of the band pass filter 14 arepositioned so as to be farthest from the opening 2 a, there is a lowpossibility that the second parts 15 b covering regions of the tightemitting surface 14 b facing the corner regions 14 e cover a region ofthe light emitting surface 14 b facing the light transmission region 10a. Moreover, the bonding members 15 at the respective corner parts ofthe band pass filter 14 are separated from each other. As describedabove, in the light detection device 1G, the bonding members 15 are notarranged at a region of the light incident surface 14 a of the band passfilter 14 excluding the corner regions 14 e but is arranged at thecorner regions 14 e.

Also in the light detection device 1G, like in the light detectiondevice 1D as described above, the band pass filter 14 forms a lighttransmitting unit 100. That is, the light transmitting unit 100 includesthe band pass filter 14 that transmits light incident on the lighttransmission region 10 a of the Fabry-Perot interference filter 10.

[Actions and Effects]

As described above, according to the light detection device 14 the bandpass filter 14 can be caused to function properly like the lightdetection device 1D described above. Moreover, in the light detectiondevice 1G, like the light detection device 1D described above, lightdetecting characteristics are improved.

Furthermore, in the light detection device IQ the band pass filter 14 isfixed to the inner surface 6 a of the top wall 6 by the bonding members15, and the bonding members 15 are not arranged at a region of the lightincident surface 14 a of the band pass filter 14 facing the innersurface 6 a of the top wall 6 excluding the corner regions 14 c but arearranged at the corner regions 14 e. According to this configuration,since the bonding member 15 is not arranged in a region of the lightincident surface 14 a of the band pass filter 14 excluding the cornerregions 14 e, scattering and diffraction of light and the like at thebonding member 15 are more securely suppressed.

[Modifications]

Although the third embodiment, the fourth embodiment, the fifthembodiment, and the sixth embodiment of the present disclosure have beendescribed above, one embodiment of the present disclosure is not limitedto the respective embodiments described above. For example, thematerials and the shapes of the respective configurations are notlimited to the aforementioned materials or shapes but may employ variousmaterials or shapes.

Moreover, in the respective embodiments, the bonding member 15 may notprotrude outward from the outer edge of the band pass filter 14 whenviewed from a direction parallel to the line L. In each of theembodiments, the second part 15 b of the bonding member 15 protrudingoutward from the outer edge of the band pass filter 14 may not extend tothe inner surface 5 a of the side wall 5 and may be separated from theinner surface 5 a of the side wall 5. For example, in a case where amaterial of the bonding member 15 is light transmitting resin, from theviewpoint of improving the fixing strength of the band pass filter 14 tothe inner surface 6 a of the top wall 6, it is preferable that thesecond part 15 b extends to the inner surface 5 a of the side wall 5.However, for example in the case where a material of the bonding members15 is a low melting point glass or a resin having a high hardness, fromthe viewpoint of preventing a crack from occurring in a bonding member15 due to a stress acting on the bonding member 15 from the side wall 5,it is preferable that the second part 15 b does not extend to the innersurface 5 a of the side wall 5.

Moreover, in the third embodiment and the fifth embodiment, thethickness of the second part 15 b of the bonding member 15 in thedirection parallel to the line L may be the maximum at a part in contactwith the inner surface 5 a of the side wall 5 depending on the viscosityof the bonding member 15. As a result, for example at the time of curingthe bonding members 15, it is possible to suppress occurrence of a crackin the bonding members 15 at parts corresponding to the corner parts 14d of the band pass filter 14. Furthermore, the bonding member 15 isprevented from reaching the light emitting surface 14 b of the band passfilter 14.

Moreover, in the fourth embodiment, the fifth embodiment, and the sixthembodiment, since a bonding member 15 is not arranged in a region facingthe opening 2 a on the line L, a material of the bonding member 15 maybe a material that does not transmit light.

Furthermore, in the sixth embodiment, after the band pass filter 14 isfixed to the inner surface 6 a of the top wall 6 by the bonding member15 arranged in the corner regions 14 e, the bonding member 15 may befurther filled between the inner surface 6 a of the top wall 6 and thelight incident surface 14 a of the band pass filter 14 from a region ofthe outer edge of the band pass filter 14 where the bonding member 15 isnot arranged when viewed from a direction parallel to the line L. Notethat, at this time, the bonding member 15 is prevented from entering theopposed region of the light incident surface 14 a of the band passfilter 14 facing the opening 2 a.

Moreover, the shape of the band pass filter 14 is not limited to arectangular plate shape and may be a polygonal plate shape. In that casealso, the band pass filter 14 is positioned with a high accuracy by therespective corner parts, and the band pass filter 14 becomes less likelyto be affected by heat from the package 2. Therefore, even in a casewhere the band pass filter 14 has a polygonal plate shape, the band passfilter 14 can function properly.

Furthermore, depending on the type of a light receiving element used asthe light detector 8, the band pass filter 14 is required not only cutsoff multi-order light having an order higher than or equal to threeappearing on a shorter wavelength side but also to cut off lightappearing on a longer wavelength (for example, a=1) side. That is, in alight detection device for obtaining an optical spectrum with respect toan A-th order light (a=A), it is necessary to cut off both higher orderlight (a>A) appearing on the shorter wavelength side and lower orderlight (a<A) appearing on the longer wavelength side.

Moreover, the package 2 is not limited to the CAN package as describedabove and may be any package as described in the following. That is, thepackage 2 may be any package as long as the package includes a firstwall part formed with an opening 2 a, a Fabry-Perot interference filter10, a second wall part facing the first wall part with a band passfilter 14 and a light detector 8 interposed therebetween, and acylindrical side wall part surrounding the Fabry-Perot interferencefilter 10, the band pass filter 14, and the light detector 8.

REFERENCE SIGNS LIST

1A, 1B, 1C, 1D, 1E, 1F, 1G . . . light detection device, 2 . . .package, 2 a . . . opening, 3 . . . stem (second wall part), 5 . . .side wall (side wall part), 6 . . . top wall (first wall part), 6 a . .. inner surface, 8 . . . light detector, 10 . . . Fabry-Perotinterference filter, 10 a . . . light transmission region, 11 . . . leadpin, 12 . . . wire, 13 . . . light transmitting member, 13 b . . . lightemitting surface (inner surface), 14 . . . band pass filter, 14 a . . .light incident surface, 14 c . . . side surface, 14 e . . . cornerregion, 14 f . . . opposed region, 15 . . . bonding member, 35 . . .first mirror, 36 . . . second mirror, L . . . line

1: A light detection device, comprising: a Fabry-Perot interferencefilter having a first mirror and a second mirror, a distance therebetween is variable, and provided with a light transmission region on apredetermined line, the light transmission region configured to transmitlight corresponding to the distance between the first mirror and thesecond mirror; a light detector arranged on a first side of theFabry-Perot interference filter on the line, the light detectorconfigured to detect light transmitted through the light transmissionregion; a package having an opening positioned on a second side of theFabry-Perot interference filter on the line, the package configured toaccommodate the Fabry-Perot interference filter and the light detector;and a light transmitting unit arranged on an inner surface of thepackage so as to close the opening and including a band pass filterconfigured to transmit light incident on the light transmission region,wherein, when viewed from a direction parallel to the line, an outeredge of the Fabry-Perot interference filter is positioned outside anouter edge of the opening, and an outer edge of the light transmittingunit is positioned outside the outer edge of the Fabry-Perotinterference filter. 2: The light detection device according to claim 1,wherein the light transmitting unit further includes a lighttransmitting member provided with the band pass filter, and an outeredge of the light transmitting member is positioned outside the outeredge of the Fabry-Perot interference filter when viewed from a directionparallel to the line. 3: The light detection device according to claim2, wherein an outer edge of the band pass filter is positioned outsidethe outer edge of the Fabry-Perot interference filter when viewed from adirection parallel to the line. 4: The light detection device accordingto claim 2, wherein a thickness of the light transmitting member is avalue larger than or equal to a value obtained by multiplying a distancebetween the Fabry-Perot interference filter and the light transmittingmember by 0.5. 5: The light detection device according to claim 2,wherein the Fabry-Perot interference filter has a silicon substrateconfigured to support the first mirror and the second mirror, and thelight detector has an InGaAs substrate formed with a photoelectricconversion region. 6: The light detection device according to claim 2,wherein the band pass filter is provided on a light emitting surface ofthe light transmitting member. 7: The light detection device accordingto claim 2, further comprising: a lead pin penetrating through thepackage; and a wire electrically connecting a terminal of theFabry-Perot interference filter and the lead pin. 8-16. (canceled)